Just 24h until SofoBoMo 2010 officially starts. Expect an official announcement on the SoFoBoMo website when it happens.
Of course you can start any time in the 2 month window, as long as you're finished and submit your entry by the end of 31st July. If you want to get full advantage of the 31 day window, don't start any later than 1st July.
For my part, I'll be starting next Sunday 6th June, I expect. That gets me in early and gives me chance to get in a second book if the opportunity arises (although I'm not expecting it to do so).