Its coming and soon.
Description of how it affects DODS, TF2, CSS and HL2MP
Players: Good idea to back up your custom files before the conversion.
Mappers: Read up on the new file and directory information
Server Operators: Opt into the beta now if you can and learn the ropes
Read the Server Op Faqs and keep up with the HLDS mailing list
TF2 Beta bugs are being reported here
Beta players can only play on Beta servers for all games