My Experiences with L4D2 Beta on Linux, so far...
So far, the beta seems to be coming along rather nicely. However, it's still got some problems and some that are not affecting the stable Windows release (that I am aware of). Some of the following issues may be posted elsewhere, but since we have no official bug tracker, I'll just list everything I've noticed, as I notice it.
* c2m5_concert rescue vehicle arrived on spawn of second finale tank. (single player/localhost)
* Mouse input location for vocalize radials erratic.
* Raw mouse input is extremely slow and erratic.
* -high launch parameter causes extremely low framerate (15 fps, for me)
* Occasionally, two mouse cursors appear on menus or Steam overlay, each tracking differently. (Noticed this on Killing Floor, as well. Looks like a Steam Beta bug, perhaps?)
* Occasionally, combat shotgun audio becomes muffled. Switching weapons and back fixes.
The game is very playable on Linux on my low-end PC (even though there is never anyone online in the beta servers) and very enjoyable so far, outside of the above mentioned bugs and annoyances. I look forward to when it is stable enough for a proper release.
I will post my system specs and L4D2 config tonight, for more information.