Long story short - excellent!
SSAO 8/medium, Smoothing (antialiasing) disabled and all of the rest maxed out (on high) -> smooth gameplay, 25+ FPS, often 30+.
Smoothing disabled because it severely reduces FPS* and I play on 1680x1050 (full-screen) 15" display (high pixel density).
Vertical synchronisation - haven't tried it because I didn't notice any tearing nor stuttering.
It's worth mentioning that the initial automatic settings the game chose itself were very good. I only changed shadows quality from Medium to High and the resolution to max+full-screen of course.
Gamma control works. I've seen reports on problems with it.
No crashes, no freezes, no sound stuttering etc. The game would seem so polished if not for the ugly-ass fonts
System and hardware details:
Fedora 18 default, gaming done on installed
LXDE ** session for better performance.
Catalyst 13.1 legacy proprietary driver (no settings altered)
AMD Mobility Radeon HD 3650
256 MB RAM
Core 2 Duo 2.53 GHz
8 GB
Audigy 2 ZS Notebook
Lenovo Thinkpad T500
* same on Trine game so I'd suspect the drivers/hardware rather than implementation in Amnesia.
** LXDE gives ~2 times better gaming (3D) performance on my system in comparison to Unity and Gnome Shell.