I actually recently used a Microsoft Wireless Explorer until recently, and I hated it... it was very slow, and the delay (from when you move it to when it registers) was very, very
noticable. I even played GTA: SA with it, and it wasn't too bad--but it made aiming relatively harder since you had to start thinking a half second in advance of where you wanted your pointer to go.
Right now, I'm actively using the MX1000, and its literally so sensitive I can't even tell its a wireless mouse... in fact, its more accurate than my wired optical mice, probably due to the fact that its a laser instead of a normal light. Either way, the first day I plugged it in, I thought it was TOO sensitive. Fortunately, adjusting pointer speed and acceleration made it much better.
Plus, I haven't charged it in 2 days, and its still got a full battery--and this is with decent usage (although not gaming quite yet).