I (and others) have done similar, extensive analyses in
this thread, with most recent analysis
here.
I'd disagree with you on a few places here and there...
Iowa is safely Democratic this year, despite their recent taking of the state.
As brittain mentioned, Louisiana is (at best) Lean GOP.
Heath Shuler appears to be safe, so North Carolina is Safe Democratic.
And I'd put WY-AL more to "Lean Republican" than "Tossup," personally.
By my estimation,
Safe D: 20
Likely D: 2
Lean D: 3
Tossup: 8
Lean R: 3
Likely R: 6
Safe R: 8
(With certain states in there being possibilities of tossups, etc.)
Republicans would need a
very good day to win without defections, though they could (on a reasonably good day) force a deadlock.
As for defections...it's unlikely in any currently Democratic-held state, with a couple of exceptions. (If they take someplace like Alaska, Louisiana, or Alabama, there may be some temptation--freshmen anywhere in red districts in red states may feel vulnerable or feel an obligation to vote for who their district voted for).
Note also that Representatives can affect the vote of their state by simply declining to vote...this can often tip the balance of the state without the person having to vote for the candidate of the other party directly.
The main exceptions being:
Herseth-Sandlin, Davis, and Castle, as mentioned. Herseth-Sandlin also pledged to vote for the winner of her state in the event of a tie in 2004.
I wouldn't be surprised if there were at least one abstention in Indiana, as well, unless the state was exceptionally close.