Firmware 3.21 will disable the 'Other OS' option on the original PS3s (not Slim models), and will be available from April 1st.
Those that use the 'Other OS' feature can choose not to update to 3.21, but the following will not be available to them (until they upgrade to 3.21)..
* Ability to sign in to PSN and use network features that require signing in to PSN, such as online features of PS3 games and chat.
* Playback of PS3 software titles or Blu-ray Disc videos that require PS3 system software version 3.21 or later.
* Playback of copyright-protected videos that are stored on a media server (when DTCP-IP is enabled under Settings).
* Use of new features and improvements that are available on PS3 system software 3.21 or later.
Link to PS Blog (EU) entry:
http://blog.eu.playstation.com/2010/...ing-april-1st/