I'm a Justine fan, but I still don't think that the title is automatically going to be hers. Threats to her:
Kim. Yes, Justine's just beaten her on hardcourt, but I still think that Kim is the better hardcourt player overall and could beat Justine in the final. That said, Justine is very tough in finals (just look at her record in them this year) and Kim seems to be weaker (not weak, just weaker).
Lindsay. Former champion here, lots of experience, definitely had the game to beat Justine on hardcourts. Those deep groundstrokes would keep Justine pinned back to the baseline.
Jennifer - former GS champion, lots of hardcourt experience, should be motivated, playing pretty well at the moment. I think Justine should win this matchup if it happens, but it won't be easy and there's at least a 30% chance of an upset.
Elena Dementieva - playing very well at the moment, a more natural hardcourt player than Justine, and someone she's always had trouble with. I think she poses quite a serious threat to Justine, and she's got to fancy her chances of getting to the final and even winning the thing if she gets past Justine, so she must be motivated.
Amelie - I'd like to see her do well, but given that she's on the other side of the draw, her chances of coming through to face Justine are relatively small. If she does do so, it'll be fantastic match.