Kim has a great game, no denying that. I just feel that there are other players who are ahead of her in terms of results at a slam. I mean in terms of consistency, there are few players who have done better than Kim. I think in this conversation, you have to consider Justine, Amelie, Nadia, and Venus (yeah I know, VENUS), as other favorites for the title as well. Here's why:
When Justine is healthy, there really are 3 players who can, at a decent level, challenge Justine on clay: Jennifer (who's indefinate), Amelie (I just think her game matches up well), and Serena. She's won RG more times than any other active player, and it looks like she is timing her events well enough to peak for those all important 2 weeks at the end of May.
Mauresmo is probably the best clay courter not to have won the French. She has won at least one clay tournament a year for the past 3 years. Kim hasn't won a clay tournament (before Warsaw) in nearly 3 years. But we'll see how far the breakthrough win in Australia goes to silence her slam demons and get her through seven matches at home.
Nadia is on a great run this year on clay, and I think that once she got over the hump of not winning a title, she will definately be a contender. I mean, even while she was battling her demons, she got to 2 RG semis in the past 3 years (more than anyone not named Justine). It will be interesting to see how she handles the pressure of having the biggest clay streak this year at Berlin where a decent field (bottom half excluded) is waiting to end her streak. She should get to the finals easlily, but what she does once she gets there should definately solidfy her chances as a contender.
When it comes down to slam time, you really can't count out Venus. Yeah I know she lost in the 1st round of the Oz, but if you look at her record at slams, whenever she loses in the first round of a slam, she comes back to the next one on a mission. (1st round Wimbly loss  followed by F at US Open on DEBUT! 1st round French loss  followed by 2 straight slam wins). She has Richard back in her corner, and she's looking to turn things around. If she stays healthy, look for her to make some noise as well.
I think this is the first time since 2003, where there are a few decent contenders for the title. Kim is a great player and VERY consistent, but a few things will determine whether she can get that second slam at the French or if she'll have to wait for another hardcourt slam (my prediction for where she'll win another one).
Career Grand Slam in your 20s? Been there done that. Career golden slam your 30s?
There's only 1. Serena.