How do I copy Team Fortress 2 to other computers?

Since Team Fortress 2 is available for free, many of my friends have downloaded the game. Can I copy the game on a digital media (USB stick or external hard drive) without creating a problem with Steam? This will save me almost 6GB download.

EDIT: I said that this transfer must be made between two different user accounts.

The easy way to do it would be to use Steam's backup feature. Select "Steam" on the menu bar, then "Backup and Restore Games...". Choose "Backup currently installed games", after which you can pick TF2 then point the backup utility at your thumbdrive to save. (It tells me it will be 6999 MB, which suggests that it compresses the backup, which may also be why some said it takes longer than just copying.) To install on other computers—restore—go to the same menu item and just pick "Restore a previous backup"

You could also just copy the team fortress 2 *.gcf (and probably the source *.gcf, and maybe the half-life 2 *.gcf's...) files out of the \steamapps folder and put them on to the computer where you want to "install" the game.

Other online sources, such as the Valve Forums, have specified these files as being the core ones:

multiplayer ob binaries.gcf
orangebox media.gcf
source 2007 binaries 2.gcf
source 2007 binaries.gcf
source 2007 shared materials.gcf
source 2007 shared models.gcf
source 2007 shared sounds.gcf
source engine.gcf
source materials.gcf
source models.gcf
source sounds.gcf
team fortress 2 client content.gcf
team fortress 2 content.gcf
team fortress 2 materials.gcf

Total size: ~11.0 GB

The files in /steamapps/[username]/team fortress 2 are reported to be 'personal' stuff, screenshots (prior to a recent update), keybindings, crash reports, etc.

You could actually copy the entire /steamapps folder, or at least all the *.gcf and *.ncf's Unless you're hard-pressed for time, I'd just use the backup/restore, as it's all but guaranteed to work.