Obama plans to declare victory May 20 - Yahoo! News
In summary: May 20th, Obama plans to declare victory, assuming nothing changes, based on a needed delegate total of 2,025 that excludes florida and michigan (which, to be fair, is the official DNC number this year). Clinton plans to contest it, based on a needed 2,209 margin including the two stripped states. The kicker is Obama most likely will not have 2,025 delegates at that point, but rather a simple majority of the possible pledged delegates.
I foresee this getting VERY ugly. :/