(This is with the Linux 64-bit Beta 3 Demo, not the full version.)
CPU: "Intel(R) Pentium(R) 4 CPU 3.00GHz" (Dual core, family 15, model 6)
RAM: 1 GB DDR2, which is never enough.
Video: NVIDIA Quadro NVS 285 (This is garbage. It's like a GeForce 6200.)
Video drivers: nouveau/Gallium 0.4 on NV44/OpenGL 2.1 Mesa 9.0.3/GLSL 1.20
Audio: Advanced Micro Devices [AMD] nee ATI SBx00 Azalia (Intel HDA)
OS: Ubuntu 12.10 64-bit running xubuntu-desktop.
X.Org version: 1.13.0
Everything is in slow motion. When I shrink the window to postage stamp size, it's less slow. The game usually runs at ~20 FPS with a big window, and ~40 FPS in a tiny window. Otherwise, things seem to work OK.
Console dump is mostly like this:
Event update took 0.006057
Draw took 0.036458
Framerate: 29.649
Event update took 0.005426
Draw took 0.029369
Framerate: 28.3728
I tried this with the NVIDIA proprietary drivers, and the game was practically unplayable with strange stop-and-go behavior - but with those drivers I get it with other OpenGL software, too. There's probably no need to worry about that.
Luckily I'm not SOL - I've got a perfectly nice dual Xeon workstation running Windows, and that handles Knytt Underground just fine. If the game simply will never run properly on my machine given its modest specs, that OK.