Tim Kaine is just too good a fit for the Obama ticket to pass up. As attractive as cadidates like Kathleen Sebelius might be, one minority on a ticket is plenty given that there has never been a winner with a minority on the ticket. Speaking of minorities, Kaine's fluence in Spanish will aid Obama in that group of ever-growing importance. The cherry on top, of course, is that Kaine is from Virginia, and all important battleground state, and having him on the ticket will make it a strong Obama state.
Obama/Kaine. Get used to it.