The only reason Romney is doing reasonably well is
1. He has flip-flopped on a lot of issues and some people buy his excuses
2. He is one of the few independents
3. He debates well
4. There are no other good contender, yet!
Romney is still really unpopular among republicans. That's why they are looking for another candidate. Their next attempt seems to be Herman Cain, since Rick Perry failed. Cain looks stronger now, especially when Perry has been such a disappointment.
If Cain wants to win he really needs to keep his performance up, because his credentials are not impressive. Also, Perry better not improve his performance, because then he's toast.