Now that the Media Portal 1.0 RC3 release has been available for several weeks and the HD-PVR now works with Media Portal, the MediaPortal crew has been busy working out any remaining bugs in that release. Just before Thanksgiving they released RC4 with a bunch of bug fixes so if you're using Media Portal RC3, be sure and get your update.
The final release is set for sometime before Christmas 2008.
Changelogs for RC4:
Changelog: MediaPortal 1.0 RC4
Changelog: TV-Server 1.0 RC4
Changelog: DeployTool 1.0 RC4
Read More at MediaPortal Website