I am using the MS Elite and it is awesome. I bought it for $100 at Best Buy during the Columbus Day sale with a coupon. I cannot perceive any lag with either the mouse or the keyboard. My keyboard did however disconnect for some reason, but I just pressed the little button on the receiver and the keyboard and it reconnected just fine, and it has only happened once. The base reciever was sitting right next to my cable box and my wireless router so I'm sure that had something to do with it.
As far as the horizontal tilt, it doesn't really work that great. It doesn't scroll smooth (jumps/steppings) and it is painfully slow. The vertical scroll is vast improvement though. With other mice, the scroll wheel would jump down 2 to 3 lines which made reading articles or studying fine details on a website a pain. The newer mouse scrolls more naturally without the big jumps of other mice, but I can still notice just a tiny stepping. Very minimal that it doesn't bother me at all.
The keyboard is great too. The scroll wheel on the keyboard is very convenient and so is the back and forward buttons. I wish they had a track pad on the keyboard though, then you could surf and type without ever having to move your hand over to the mouse. One thing I noticed about the scroll wheel on the keyboard is that it isn't like the scroll wheel on the mouse which also serves as a button to switch between tasks. I kept banging my thumb against the keyboard's scroll wheel until I figured it out, DOH! I wish they would have made the scroll wheel function consistent across the set. You can also program up to five websites as favorites. Just press the number for five seconds and you've set that site as one of your five favorites. It's as easy as programming your favorite radio stations in the car. All the other keys are nicely placed too except of the right CTRL button and what the heck happened to the INSERT button? MS moved the INSERT button function to the Print Screen key. I guess they thought people could use the DELETE button more. The right CTRL is closer towards the center of the keyboard to save some space so I keep missing it whenever I type, but I'm sure I'll get used to it soon enough. One major gripe, why can't MS give you an option to have the F LOCK on whenever you boot the computer. I find the Enhanced Function Keys redundant and useless. I want my Function keys back!
This is coming from somebody who bought a MS Bluetooth set just a month before. The lag was killing me. That and the fact that you can't use the set in DOS, Other OS, or even BIOS Setup makes the MS Bluetooth a poor product. If you are in the market for a new set, definitely consider the MS Elite. They also say that the batteries MAY last up to six months, but I've just had mine for a few days. We'll see...