You're getting yours a day ahead of me. I ended up getting the 8G RAM upgrade from Apple, then ordering an additional 8G RAM from OWC (actually saves about $50 doing it that way). I've seen the reports of the new MP doing better with 6 sticks or RAM instead of all 8, but I'll be using it for music, so I'll probably end up using the full 16G of RAM.
...until 4G RAM prices drop, anyway.
I ordered mine from Macconnection.com - they discount it slightly ($110) and don't charge sales tax to this California resident. This will be the 3rd Mac I've bought from them. They're a good vendor.
I opted for 12GB based on the benchmark results that have been posted so far. My primary memory consumer will be VMWare virtual machines - I have a Windows Server 2003 VM that is running SQL Server, IIS, and the Cognos 8.x server components that needs some room to stretch its legs. I expect Lightroom and Photoshop will be a lot happier on the new machine than they are on my 3GB MBP too.