As awaited SP2 was released this week. There are (luckily) no kernel changes in SP2 so the upgrade path should be much smoother than SP1.
News are replacing RIS with WDS, WPA2 support, icacls an updated version of Cacls that correctly propagates inherited ACLs (hmmm sounds like a song we've heard before) etc. For a more comprehensive list of new functionality look here.
SP2 for x86
SP2 for x64 (Also used for Windows XP x64 edition)
SP2 for Itanic