So people are really throwing out that she should be recast? That's pretty messed up. Do you guys really want MJ cast purely on who most people want to bang? Firstly, that's a sad debasing of the character, basically saying "she was a model/actress, so she's just hot" rather than the great complexities her character has. Secondly, they could have gone with an MJ who is more like the Ultimate version, where, yes, she is beautiful (as is Shailene Woodley), just not in the I wear tight, short dresses flaunting all I got kind of way (also not really MJ, even in her early party girl days) but is also becomes a really good friend of Peter's and is rebellious and interested in becoming a reporter.
And I say this as someone who really doesn't like MJ all that much. But to just go "no, not hot enough" isn't a good reason to slam a talented (and still plenty attractive) actress from being worthy of the role.
Also, Shailene Woodley is going to be the star of Divergent. That book is pretty huge, with its popularity just slightly below Hunger Games with the teen reader crowd. If that movie is good and successful, which I hope it is, you're going to see this woman explode much like Jennifer Lawrence did with the one-two punch of X-Men First Class and Hunger Games. Chances are, if they do recast and not just hold off her role, that Sony will be kicking themselves for losing her.