Actually, every day is an open source day for me @ Microsoft (since that's what I do -- publish and promote open source SQL Server projects), but tomorrow is a special all open, all source, all day day for us.
Tomorrow the bonus for me is being able to sit back and watch for most of the day while the Microsoft Conference Center hosts an all day series of presentations by Other People™.
I'll be the guy wearing the SQL Heroes T-shirt. Feel free to say, "Howdy."
[Yes, Steve (all of the Steves), I'm still working on MDDE, SQL Server Gadgets, updated AdventureWorks installers and 19-zillion other things that you want updated on CodePlex. There're only three of us on this little team. Thank you for your patience.]