Continuing today's political slant, my first reaction to this news was to channel Hillary Clinton. Miami absolutely does not need Stephon Marbury mucking up the point guard position.
Marbury is one of those dudes I kind of like as long as I don't have a rooting interest in the team he's playing for. I've been a quasi-fan of Marbs since the Twin Cities era. But at this point in his career, he'd be a colossally boneheaded pickup for the Heat.
You can't go into camp with four point guards, particularly when none of them can play shooting guard, none is shaky enough to be sent to the D-League and none would make sense to trade. Marcus Banks' contract anchors him here unless it's in exchange for a worse contract (Jamaal Tinsley). Chris Quinn and Mario Chalmers are young, and it would be remarkably short-sighted to trade a young point to clear room for an old point who wants to end his career on another continent.
Marbury gets in the way of Dwyane Wade, Michael Beasley, and Shawn Marion offensively, and doesn't get in anybody's way defensively. Signing Marbury would be an escalated version of the Jamaal Magloire signing: that was just a harmless big man to plop on the bench, while this would hand over the offense to an unstable former star with selfish tendencies. The risk is almost nil with Magloire, but huge with Marbury. He could piss off Wade and impair Beasley's development, and would certainly slow down the progression of Chalmers and Quinn.
On the other hand, there's...nothing. I can't think of a single good reason to sign him. Miami's not set at point guard by any means, but we're not this desperate.