First, 538 says so, and Nate Silver knows his statistics.
Second, I give you the dramatically intensifying pre-election Republican circular firing squad.
The thought of being both, at this point, pretty much a straight-ticket Democratic voter and simultaneously believing that our guy is going to win the Presidency is unusual. Surreal, even. So I don't post this lightly, or out of a sense of hubris.
But Obama is leading every single Kerry state by double digits. Those states (the West Coast, the Upper Midwest [MN/MI/WI/IL], and New England) = 252 electoral votes. 270 is the magic number. Add to those states IA, NM, and CO, where he is leading comfortably, and he's already at 273.
That's before even considering FL, OH, NC, VA, WV, MO, IN, NV, ND, MT, GA, or AZ (!), some fraction of which will go to Obama. That fraction will equal Obama's mandate. NV and VA are pretty much already in Obama's column; FL, OH, NC, MO, IN are all toss-ups. If Obama can flip any one of ND, MT, GA, and AZ, the rout will be on.
Honestly appraising the aggregated polling data, Obama looks likely to be the first Democrat to crack 50% of the popular vote since LBJ in 1964. He would have a Senate majority of roughly 14-15 seats (give or take) and an imposing House majority somewhere north of 50 seats.
That reminds me, I need to go get some champagne....
P.S. For what it's worth, the Obama folks are definitely not taking anything for granted....