I've had the logitech G7 for years and it has been a very good "wireless gaming" mouse. I personally don't notice any lag, but I generally play RTS and MMORPG games where tiny lag isn't an issue. I always use wired Keyboards, but not wired mice. I really can't stand wired mice.
Sadly, my G7 is starting to develop a double-click problem that has been reported a lot with this mouse. I think i'll check out the Sidewinder X8 to replace it. That charging system is pretty cool. On the G7, you have to remove a battery and swap it with the second battery, then put the dead battery back in the charger. Pretty annoying...especially when you have two dead batteries, and thus no mouse.