tehh4ck3rkirbyMake sure to back up your maps, configs, hud, etc. before you forget!
+1. Steampipe conversion will wipe all your maps, scripts, configs, huds, etc. so make sure to back them up.'
EDIT: Also, the switch to Steampipe is going to break the SDK, so mapmakers beware.
Actually you only need to backup your cfg files.
All of the custom map, hud, sound, material files will be moved to tf\download folder in the new tf2 steampipe folder (which is located at <your account name>\common\team fortress 2\tf\download\)
What you need to do after the conversion is done:
1. Copy back your cfg files to new tf folder
2. Create a new folder in <your account name>\common\team fortress 2\tf\custom\<your folder here> (could be anything eg. mycustommods)
3. Move all files and folder in the <your account name>\common\team fortress 2\tf\download\ (which should be including maps, huds, custom sounds, models, materials)to the new folder you just created - mycustommods)
4. Profit.