I heard about the motion control improvement before I actually did the update, and wanted to test it back to back.
The best game I could think of was Formula 1. I remember trying the motion control way back when the game came out. I found that it was actually rather nice for free lapping, but when trying to thread the needle in a full field of opponents, the lag became an issue and a liability.
So I tried the motion control option again and I found it actually wasn't as bad as I rememebred. Lag (and when I say "lag", it brings with it a measure of inaccuracy. Not just the delay itself.) was definitly detectable, but mostly just for subtle adjustments.
I then installed the update and tried again. Immediatly noticeable difference. Improved accross the board. I played for hours - the most I've played since it came out. I usually am too lazy to drag out the Driving Force Pro wheel and play this game properly, as F1 demands some serious accuracy and finesse... and demands it be snappy! With the improved motion controls, the game is totally playable with just the Sixaxis. I wont be going back the steering with the stick anytime soon!
So yes, the control has been improved significantly.
Oh. And the browser is faster. Still slow as hell.... but a bit faster.