Tweaking aside there are some services that I dislike, the biggest two are:
The craptastic service that comes with some of creative drivers (can't remember its name), the one that breaks the autoplay.
"Machine Debug Manager" that for reasons i never understood is included in some version of office express install (NO i do NOT wish to debug you &%$@^&%$ [mumble] most #$@& annoying error message ever [mumble]).
And hmmm... I always hated the index service, some wasted memory and cpu cycles every once in a while is nothing to get excited about, but attaching some redundant additional i/o to every i/o operation in an out-of-the-box installations when most application don?t even use it, always annoyed me.
edit
Now I have to mention this:
I cant remember who it was but this one guy (i think he was an accountant) that pressed 'yes' on the "do you wish to debug" window, call me and said ""come quick, windows just want mad or someting", I distinctly remember VNCing his system and seeing the VB debugger when he said "I can see the inside of windows".