And HRC will endorse Obama, too

Not only will she drop out, but she'll endorse Obama. And it's her supporters that pushed her out, according to NBC's Andrea Mitchell. Moreover, according to Howard Fineman, the veep-mare is not going to happen. Update: According to Clinton's campaign, the event will take place on Saturday:

Senator Clinton will be hosting an event in Washington, DC to thank her supporters and express her support for Senator Obama and party unity.  This event will be held on Saturday to accommodate more of Senator Clinton's supporters who want to attend.