I've got Windows 7 - 64 bit Ultimate running on my HP quad core laptop with 8GB of RAM and it's running great.  Here is a list of what is currently running, what I'm doing and a pict of the current task manager performance graph.  It's not even up to 50% capacity.  Sweet... 

• Internet Explorer 8.0 - Adding blog entry
• Outlook - checking email
• Windows Explorer - backing up files to my server, FTP'd to remote server and copying files
• Live Messenger - instant messaging friends
• Microsoft Online Services
• Windows Virtual PC - Windows XP vpc which is VPN'd into client network, running remote desktop connected to remote server, running SQL Server, Analysis services, and VS2008
• TextPad
• Paint.NET - editing photo
• Snipping Tool - screen capture
• Win Amp - playing my MP3s with visualizations rendering
• SQL Server Management Studio - connected to SQL Server 2008, running queries
• Visual Studio 2008 - working on SSIS project