I thought they fixed that framerate issue... I thought it was one of the first things they did in v1.1. My memory's terrible, though, so there's no telling.
The only mouse input concern that's left is one that's unique to UT3 that many people can feel but no one can really explain or fix. The mouse input system just feels
off to many people (myself included) -- no other way to put it. Every other game I've played in the past five years has been perfectly fine with regards to the mouse, so it sticks out as obvious when there's one that's different in any way.
Other than that UT3's netcode is the worst of the UT series (barring UT, but I never played that online in any capacity). Not only does it have inaccurate client-side projectile interpolation (like all UTs) but it's also got hitscan inaccuracy issues as well, something unique to UT3. Plus all pings are higher than past UTs.
Screwed up input system + bad FPS + bad netcode + higher pings = Hyru suckage.