This will no longer work as of the SteamPipe update on May 1, 2013. See here to learn about the SteamPipe update.
This utility will not be updated.
Include this file with any skins/mods, or download yourself if you don't feel like crawling through your Steam folders.
This is a batch file that will detect the Steam directory (or prompt the user for one if in a non-standard directory), then copy the files in. It will properly work with models, sounds, maps, and other skins/mods if the modder has properly placed their directories. It is important to note that this will not work with games that have been modified to use junction points (through the use of SteamMover or manual methods), but this is far from the standard installation of 99% of Steam users.
Many modders include an archive (RAR or ZIP) that includes a folder called "tf" and a readme. Drop both of those (along with install.bat) on your desktop and run install.bat.
This file can easily be edited for other Source (ex CSS) games by right-clicking it, clicking edit, and changing the directories (change the line that starts with xcopy).
You are free to modify and distribute this file.