Lack of Steam Stat sigs... :(
I loved the BF:BC2 sigs you could get that could list every possible stat you had! :)
After looking at my Steam stats for L4D2 last night, I noticed you can see loads of detailed info like number of kills with each weapon, fave map, number of pipe bombs thrown, most played survivor, longest jockey ride etc etc. With the sheer number of stats, I'd say it is on par with BC2!
Anyway, after a bit off 1-on-1 with Google, it seems there is nowhere that can generate you a Steam game sig that lists all those details. The best I could find is a "achievements" list for a chosen game. I would have liked to show off my L4D2 stats at the bottom of my posts. :(