Take a look at this fascinating map from the New York Times, an excellent application of Edward Tufte's principles of the visual display of quantitative information (click to enlarge):
The map makes clear what Obama's electoral strengths and weaknesses are: he does well in the traditional liberal strongholds, cities and coasts, save Boston (for reasons I don't understand), LA (Latino-black division, we're told) and Clinton's New York. Look at Texas, for example: Dems have more or less won Austin, Dallas and Houston in the last few presidential elections, and lost the rural areas and the more conservative San Antonio; this mirrors the Obama-Clinton split shown on this map.
Obama does have some loyalty in the Chicago-orbiting Midwest, which means his chances of carrying swing states Iowa and Michigan are good, but it's going to be tough in Ohio, Pennsylvania, or Florida, and without two of these he's likely to lose.
On the other hand, his enormous support in the black-heavy South, together with the new Democratic registrations all over the country thanks to the hotly contested primary, might allow him to put some states in play that Bush won handily in 2000 and 2004.
Here's my electoral vote analysis, based on polling data from RealClearPolitics.com, electoral-vote.com, and intrade.com:
Obama very likely to win: 200 electoral votes
Maine at large:* 2
Maine 1st district:* 1
Maine 2nd district:* 1
New Jersey: 15
New York: 31
Rhode Island: 4
Washington DC: 3
Swing states likely to go to Obama: 38
McCain very likely to win: 149
Nebraska at large* 2
Nebraska 1st district* 1
Nebraska 2nd district* 1
Nebraska 3rd district* 1
North Dakota 3
South Dakota 3
West Virginia: 5
Swing, likely McCain: 67 total
Arkansas: 6* Maine and Nebraska give 2 votes to the statewide winner, and allow each congressional district to choose its elector independently. Nebraska is heavy Republican country, but Maine is mixed and may give 3 of its electoral votes to the statewide winner, and 1 to the loser.
North Carolina 15
South Carolina 8
Here's where it gets interesting:
Swing states impossible to call at this point: 84 votes total
Obama leads by the margin of error right now, but state went Republican in the last 3 elections, and Bush won by 5% in 2004.
Dems usually win here, but McCain leads in the polls by a hair.
Polls are a dead heat; Bush won in 2004 and 2008, but Clinton won in 1996 ('92, a three-way race with the conservative vote split, doesn't count for much), and Obama's Midwest credentials and Repub unpopularity this year puts it on the fence.
McCain leads in polls, and Repubs usually win, but Vegas has it at a dead heat.
New Hampshire: 4
Vote is extremely close here historically. Obama leads in polls by a hair.
New Mexico: 5
Same as NH.
Polls are a dead heat, and vote is extremely close historically. Vegas likes Obama, but there is a large undecided contingent in the polls, which may work in McCain's favor because Obama is more of an unknown.
Republicans usually win handily here, but polls are a dead heat, though there is a large undecided contingent.
If you award each candidate all of the electoral votes from their likely states, plus an estimated half of the swing states' electoral votes:
Obama’s predicted total: 280
McCain’s predicted total: 258
Now let's look at a few scenarios. If 2/3 of the swing state votes go to Obama, he wins handily:
Obama’s predicted total: 294
McCain’s predicted total: 244
But if 2/3 of the swing state votes go to McCain (say, roughly, Colorado, Michigan, Missouri, Nevada, Virginia), he wins by a hair:
Obama’s predicted total: 266
McCain’s predicted total: 272
So the election looks to be very close, with the advantage very slightly in Obama's favor. The question, in my opinion, is whether Obama can convince undecided voters that his promise outweighs their uncertainty about him due to his youth, inexperience, blackness, and liberalness. I think the much-vaunted conservative dislike for McCain will not play such a big role; he'll get slightly more votes then Bush in 2004 (which would indicate an even showing, since the number of voters has grown).
Meanwhile, there has been a huge increase in Democratic voter registration. I predict 68 million votes for Obama, 66 million votes for McCain, with Obama winning the electoral college 284-254.
Note that McCain needs at least 270 votes to win, while Obama only needs 269, because in a 269-269 tie (or any other situation in which no candidate gets a majority of the 538-member electoral college), the (Democratic) Congress resolves the dispute in a vote, and Obama wins.
With that optimistically said, my big fear as the general election campaign begins is an ad, run by a well-funded conservative group that's ostensibly independent of the McCain campaign, that would go like this:
[White woman in driver's seat of minivan; a daughter and son, 10 and 8 years old, in soccer uniforms, run away from minivan]
Kids: Bye, mom!
[She begins to drive away; camera shot is from passenger's seat, cinema verite-style, looking up from lap height]
Mom: [chuckles] Look at 'em go. You know, I have to keep reminding myself, this election isn't really about me. It's about them.
I like a charismatic speaker as much as anybody, and I like hearing Obama speak. But when it comes down to it, what do I really know about the guy? I never heard his name until last year. His campaign says it's no big deal that he went to a Muslim school. [Winces and shrugs] If they say so!
His minister, saying all those crazy, awful things? For years, and I'm supposed to believe Obama doesn't agree with any of it?
And the drugs... I thought that one was just a rumor. But I looked into it. I don't know how they hushed this up, but he's--he's admitted he used to do cocaine. Cocaine!
Look, [raises eyebrows and nods, forgiving viewers' guilt] I believe in giving people a chance, but I'm not gambling with my kids' future. Neither guy is perfect, but I need to know what I'm getting. For them.
[Fades out. Text: Paid for by The Veterans' Committee for Public Discourse.]
It's one of the most effective strategies for incumbents and conservatives in business and politics: exploit your image of being bland but reliable by sowing fear, uncertainty, and doubt about your upstart competition. (That phrase comes from a leaked Microsoft memo outlining a strategy for defeating the Linux operating system.)
Hillary tried this kind of thing, of course, but her attacks--while despicable--were milder than the Karl Rove generation of Republican ops, and part of why they didn't erode Obama's support more was that their audience was already committed Democrats.