I have a G7 and there is no lag as far I can tell and I believe this has been tested successfully by independant reviewers. It is fast, sensitive and suprisingly light.
I have had no real problems with it and it is a pleasure to use. The battery change every couple of days is quick and easy (but still a minor hassle). Wired mice are historical artifacts as far as I'm concerned, whenever I use one nowadays I end up flapping it about and swearing.
The niggles do spoil it a bit for me, the battery changing, the lack of forward thumb button and its expensive. Its a good mouse, but for the price I would expect no flaws.
Thing is, if you're a gamer and you want wireless its still the best option i am aware of....
Chks