Charlie Crist officially announced he's going to keep us in suspense until May regarding whether he'll run for Senate or re-election as governor. This pretty much freezes up the Republican side of things until then. Rubio, Mack, and Buchanan can declare all they want, but nobody is going to be writing them checks until everyone is sure Crist won't run. So it's likely any announcement from those three will also wait till May. If he wasn't seriously considering it, Crist wouldn't cripple his party like this.
From a national party standpoint, a lock on the Senate seat might be better than a guarantee on the governor's mansion. Once the Minnesota mess is sorted out, the Democrats will have 59 seats in the Senate and have a better-than-average chance of eclipsing 60 in the midterm election. At this point, all of the "toss-up" races for Senate are for seats that belong to Republicans. D.C. Repubs will be keen to curtail any further hemorrhaging, and Crist seems to be one of their strongest Senate candidates anywhere in the nation. Plus, if Crist steps down early, Jeff Kottkamp will have the incumbancy advantage for the governor's race.
But what about our white-haired gov's White House aspirations? If Crist wants to be POTUS one day, or more specifically January 20, 2013, it doesn't make sense for him to step down as governor to run for Senate and then almost immediately declare his intention to run for president. He could hold off until 2016, but his second term as Senator would be up for election that year too. He hasn't put up big numbers in the early polls, and for reasons no one really understands, Republicans are set on returning to their conservative roots (Tancredo/Coulter '12!).
This all kind of flies in the face of Crist's image. He's the people's governor, and the people elected him to four years as governor, not to give him a platform to boost his ego and future aspirations. You have to wonder if this naked political ambition in action would help him keep his title as Mr. Popularity.