The MX1000's battery life is measured in weeks while the 700 is measured in days. It also has the 3-segment graph for battery strength. The 1000 is noticeably lighter & has the tilting side-scroll wheel.
The only bad thing about the 1000 to me is the thumb groove on the left is a little smaller/less comfortable than the 700. The 700, though, is finicky about placement in the charging stand.
I've been using Logitech mice almost exclusively since 1984. Right now, my wife uses an older 3-button wired model (I can't get her to accept a wheeled mouse), my home PC has the MX1000, and I've bought an MX510 (wired) for my spare work laptop and an MX700 for my main laptop. I use another MX700 on the laptop when working from home.
I've also switched to the wired Logitech Access keyboard. Decent feel although it's a definite departure form the IBM Model M it replaced. I don't use the extra multimedia keys; I really just want the basics. Only drawback is that whether or not the Logitech keyboard app is installed, after booting the F-keys default to their multimedia functions instead of acting like F-keys until the F-Lock button is pressed.