Would Team Fortress 2 icons add functionality to anything? No. Would a wallpaper of them be damned cool anyway? Yes. A user on the Steam forums has put them together for you to download.

Qpingu of the TF2 community - "taking days of tedious work" - packed them up into a sheet you can download at seven different resolutions. He threw the links up yesterday. The icon pack covers all achievements through the Sniper vs. Spy update, and he promises future versions to incorporate additional TF2 updates.

You can slap this down as a desktop pic, but I'm already thinking about spending a day with a jailbroken iPhone bringing these in as a custom theme. I'm sure you guys can think of other uses too. Or, like I said, it's not about the doing, it's about the having.

The Complete Achievement Icon Wallpaper Pack [Steam Users' Forums]