Con: It's a Full-Time Job.
Since she'll likely have to sign a multi-picture contract, doing two or three of these films in a row (possibly even back-to-back, the way a lot of these things are done nowadays) and then traveling around the world promoting them could put a crimp in her ability to do more prestigious films or off-beat projects like Zombieland.

Pro: It's a High-Profile Gig.
If the movie is a hit -- which it should be, unless they take their cues from the horrendous-looking Broadway musical -- it'll reflect well on her, increasing her star power immensely and giving her the freedom to do more stuff. ...When she has time.

Con: It's a Thankless Role
Playing the girlfriend to a superhero doesn't seem to offer many challenges -- at least, not the way Kirsten Dunst did it. Maybe Stone should hold out for something with a little more meat on it? Maybe she could play her own superhero?

Pro: It Could Be a Much Bigger Role With Her In It.
Sure, MJ got kidnapped by super-villains a lot in the comics, too, but she was also a tough character, who stood up for herself on her own, even when Spidey wasn't around. If the movie can land Stone, maybe the big-screen MJ can get an upgrade from arm candy to partner.

Con: It's Beneath Her.
At the end of the day, it's still Spidey's movie, so why would someone who can headline comedies take a supporting role in an action film? Aside from the big paycheck? It's why we cry when we see our favorite comedians talking to animated guinea pigs and chipmunks.

Pro: It's Okay to Slum Sometimes.
Gwyneth Palrow is a decent actress, and was a leading lady for a long time, but her career had been on hold when she signed on to play Iron Man's secretary. That worked out amazingly well, and now she's back in a starring role as a country singer. Granted, Stone isn't as established, but the principle still applies.

Does anyone love watching movies more than characters in movies? Check out this mash-up.