Deleting the primary program files is not too hard. Just right click on a shortcut, and choose "find target" to locate the files. Getting the muck out the registery is another matter, and Adobe 6 is a monster, as I had reason to find out recently. Fortunately the superfluous drek in the registry is usually harmless, and is better left untouched if you don't have a problem.
Deleting the program files (or moving them, or having a drive letter get changed) is the usual reason the uninstall doesn't work, because the uninstall program, or some information, is deleted too. The original installer program "registers" needed locations in the registry, so if that info is mistaken, the uninstaller can't work. Some uninstallers abort or crash when there is even one item mislocated or missing. To compound this, some installer programs will not run if they cannot do an uninstall first, so you can neither get rid of the program that won't run right, nor reinstall to fix it.
Programs often store other important pieces (.dll's) in the Windows directory or Windows\system directory that may or may not be used by other programs too. Figuring out what pieces those are and if they are safe to delete is humanly all but impossible. There is some kind of count kept that goes up when another program "installs" the same piece, and down when it is "uninstalled." That is unreliable because people sometimes have to reinstall a program, or attempt to uninstall it repeatedly, and both installer programs and uninstaller programs are unreliable. That's why uninstall programs are forever asking you if you REALLY want to delete certain files with obscure names, as if you knew better than it did what needed to be uninstalled.
Obviously, using the uninstaller is the way to handle uninstalling, if possible. But don't get too confident. Since I decided to trek to the registry just yesterday, I incidently found references to a little program I had recently uninstalled. It should not have been there. There are names of programs I uninstalled so many years ago I had to rack my aging brain to try to figure out what it could be. And that is just in the intelligible part, not including the seemingly infinite length encoded keys. It was astounding how "Adobe" showed up everwhere, over and over. You would almost think Adobe was keeping the registry all for itself.
So uninstallers are not very thorough about uninstalling. You see, programmers have hard time imagining why anyone would ever want to uninstall their magnificent program. The info left behind sometimes came in handy when they used to pick up your settings from a previous version so you didn't have to do it all over again. But that is becoming a thing of the past. Programs just leave the old versions in place, and ignore the old registry keys to add their own keys in the registry, no doubt because they learned from terrible experience what an unrecoverable mess their install programs made when attempting to update former versions. They don't even get the bugs out of the main program before they want to sell you the next version, let alone get the bugs out of the installer and even less the uninstaller. They say XP is more reliable than previous Windows versions. If so, it is because XP denies more things to programs that would crash the system.
Why it might be necessary for a program to put dozens or hundreds of keys in the registry with the identical root directory, I can't imagine. Programs can be easily written to run from whatever location they may occupy and not use even one registry key. That was the normal for programs with Windows 3.1. You could put the program in any directory on any disk, and it ran just the same. It didn't matter. If you wanted to get rid of a program, you just deleted it. If you didn't like where it was, you moved it. Nothing exotic or complex is required to write programs that way.
Just in case you are wondering what brought on this diatribe and retrospective, here it is. For reasons hard to explain, or even guess, XP had assigned different letters to every partition when I added RAID, one off from what they had been, so I cleverly (I thought) copied the XP partition to where I guessed it wanted to be. This was all purely a guess, but it partially worked. Unfortunately the drive letters of most things were wrong in the registry. Peculiarly, some of the drive letters WERE RIGHT even though those things were actually on the same drives which were lettered wrong elsewhere. OK, so the whole idea was a mistake to even try. It was just something I did to confirm my guess about why XP stopped where I would have signed on, yet the mouse worked and the screen saver went off and on appropriately and the HD made "swapping" noises as if XP were running. That's what makes me a computer geek. But get this: I could not install the Nvidia chipset drivers. This, even though Nvidia is normally foolproof. The install program simply exited without a notification or an error message, without doing anything. The Nvidia uninstaller would not work either. It gave an error message, even after I fixed the drive letters for the uninstaller in the registry. Evidently neither one likes the registry as it is, and neither will work. I find this amazing and absurd. There should not even be information about the drive letter in the registry. The drivers are always installed relative to the so-called "system" directory. They have to be. Why are programmers making this so convoluted?
Normally Nvidia is the best. They are reliable. Their installer is foolproof. It doesn't ask you crazy questions that even the programmer would not know the answer to. No matter what you do, it completely redoes everything that needs to be redone, and does it automatically, and it does it right. But the more relieable way to get the drive letter thing straight, is to not use the info where it is not needed instead of having the letter stuck in dozens of places.
Of course the worst offender is Microsoft. There is no reason to write the OS so it has to be on a certain drive letter to work. It should be drive letter independent, and run regardless of where it is put, with at most one reference determining its location. You would think that would be obvious. Anything else is asking for trouble. All this reinstalling Windows when the drives are re-lettered is unneeded.
As for the drive letter problem in programs, programs should not have to know where their true location is, any more than they know the true location in memory where they run. Programmers should be doing this on their own. That once was normal. Unfortunately, the system of drive letters that MS adopted way, way back lends itself to this programming deficiency, but it could be alleviated by making drive letters "virtual", like everything else nowadays is virtual. Programs would get drive letter info if they request it (probably C, but the program would be stored on any drive, on any partition regardless. OK, I'm dreaming.
Every time I look through the registry, it makes me sick. I haven't looked in quite a while. I don't like nausea. But it is more sickening than it ever was. The best thing MS could do is to "legacy" the registry.