This has been in the beta for a couple of months now, but it's good to see it go live so everyone can take advantage of it!
I should add, when moving games like this, some titles also put some pertinent files (.ncf and .gcf) directly into the steamapps folder. When moving games, ensure to make backups of these files before uninstalling in case it removes them.
For most titles, these files are small and insignificant (and re-downloading will only take seconds), but some put almost all their game content in .ncf files (primarily, the Source games - TF2, CSS, etc). Any shared files it won't remove when uninstalling, but other games are a different matter - always a good idea to backup just in case.