Guess what… it didn't happen. From Public Policy Polling:

PPP's newest Florida poll, conducted completely after the Republican convention, finds no change in the Presidential race there. Barack Obama leads Mitt Romney 48-47, exactly as he did on our last poll of the state five weeks ago.

The Republican convention being held in Tampa appears to have been a wash. 33% of voters say it made them more likely to vote for Republicans, 33% said it made them less likely to vote for Republicans, and 34% said it didn't make a difference to them either way.

There's a small bit of good news for Romney:

Romney did see a slight bump in his favorability numbers. 49% of voters have a positive opinion of him to 47% with a negative one. That +2 spread is up a net 5 points from late July when his breakdown was 46/49.

Of course, that's just ONE poll, covering Florida voters.  But it's the same story nationwide, according to Gallup.