Only recently got accepted into the beta and I was extremely eager to test TF2. You can imagine that I was a little disappointed when it finished downloading and didn't run as expected...but then it is Beta ;)
Anyway, the black screen problem appears to have been reported numerous times but with fixes primarily relating to NVidia graphics issues. I have Intel HD Integrated Graphics and the supposed 'fix' by editing /usr/bin/steam doesn't work.
I am somewhat confused however, this is a graphics only issue, I get a fullscreen blackness but I can hear sound playing i.e. the Valve loadup screen and menus ingame...
UPDATE: Here's a log from terminal when I launch TF2 and the audio is playing without video. http://paste.ubuntu.com/1402074/
Ubuntu 12.10 AMD64
3GB DDR3 RAM
Intel Integrated HD Graphics
Core i3 Gen 1 2.3GHz
Driver: Intel Open Source Technology Center Mesa DRI Intel(R) Ironlake Mobile x86/MMX/SSE2
Driver Version: 2.1 Mesa 9.0
Desktop Color Depth: 24 bits per pixel
Monitor Refresh Rate: 59 Hz
Number of Monitors: 1
Number of Logical Video Cards: 1