Bit late to the party but my 2c worth.
Decided to go full 64 bit with SQL Server 2008 R2, Server R2 & Windows 7 64 bit.
I had trouble with Office 2010 64 bit & An Excel add-in from IBM. IBM didn't have a 64-Bit solution but there was a work-around.
I had one SSIS Package that used a 32-Bit ODBC Driver. Worked out that SSIS would run in 32-Bit Mode.
Results: SQL Server & Desktop run faster and very reliable.
I'd run Windows 8 but don't think I can find a Business Reason yet as I did for Windows 7 / Office 2010 & PowerPivot.
Newer is usually better. Only real disappointments were Vista, Windows 98 SE & Windows ME.