DKCOde, forgetabout desktop sensitivity, use raw input and in windows make sure your mouse acceleration is off.
You wanna adjust the sensitivity as low as possible to suit the way you play. A good rule of thumb I picked up back in 2004 when I started playig CS and Source was to be able to do a full 180 degrees turn from the far left of your mouse pad/mat to the far right.
I think I use 1.76 sensi with my G400 with the middle DPI setting. This means I can turn quick enough if I need to on my icemat2 but also when trying to achieve a stable aim I can do so because the feel of the guns are more stable with a lower sensi, enabling you to side step double tap and then side step back and double tap. All whilst tryin to aim for the head!
Lower yor sensitivity and use settings like I mentioned and you should find you have more control.
YMMV...
Hope some o that helps.. Crouch if in trouble, if spraying aim low but most of all, try to do control bursts or even better, single or double clicks when you're targetting. You'll be way more accurate and you'll get a lot more kills that way. Use cover where you can and obviously use sound!
I'm enjoying GO and going back to Souce just doesn't feel right any more. I do wish they'd sort out a few things. Going spectate and trying to rejoin seems buggy, voting certain things when dead doesn't work. I hope they bring back skin changes for the teams. I also don't want the TAB score screen showing at round end. Seems to block what's being typed for me on my res and I press TAB enough in game to know the score by the end. Minor niggles and mostly I enjoy it.
Oh and yeh, joining servers sometimes takes me back to main menu and having to try again often solves it. That should be sorted. The whole steam server search has been shit since I can remember. Inconsistent hen it searches and doesn't, filters seem tl cause an issue and removes favourites (at least doesn't refresh them but they'll come back soon enough)...