Just in case you have not heard the great news about SQL Server's scale up capability that was annouced at the WinHEC. Well basically:
Upcoming support for more than 64 logical processors, the current limit in Windows and SQL Server. This expanded scale-up capability is planned to be released in SQL Server code named "Kilimanjaro", when running on top of Windows Server 2008 R2.
We expect to support up to 256 logical processors in this release, though that's a soft limit. The hard limits are much higher than this, but we won't support what we can't test. You'll likely see this 256LP soft ceiling get higher in each release, now that we've finally done the heavy lifting of raising the roof on Windows and SQL Server.
In case you're wondering, a logical processor is a sub-unit of a physical processor/socket/package. Typically today an LP means a core, but it can also mean a hardware thread (nee hyper-threading).
The above is information from the SQL Server Performance Team Blog - http://blogs.msdn.com/sqlperf/archive/2008/11/10/sql-server-is-movin-on-up.aspx