Everyone has already been all over this, and specifically the Suns angle. So I'll keep it short and about the Heat.
The general consensus is that it's a dumb risk for Phoenix and Miami was pleasantly surprised to have the deal fall into their laps, with the few dissenters suggesting mutual benefit and pointing to a 38 year old Kareem still "running" with the showtime Lakers. Either way, everyone is on board that that it worked out great for the Heat.
Marion will have the option to opt out of his contract at the end of this year. As good a player as Marion is, even if he does opt out, the trade will still be worth the salary dump for Miami. They have J Will, Ricky Davis, and Zo coming off the books at the end of the year. Next year's payroll with Marion will be $53 million and a mere $36 million without him.
No matter how much Marion improves the team this year, they're a lock for the lottery. It's unreasonable to think they can make up 10.5 games on seven teams in less than half the season, and somehow compete for a playoff spot.
What the Heat ultimately get out of this is flexibility. Their only priority now will be to build for the the 09/10 season, the last year of Wade's contract. They have two years to put together a team that's a contender, one that's good enough to ensure that Wade isn't tempted by greener pastures, and is happy to re-sign and stay in Miami. Saddled with Shaq's contract and his inefficacy the Heat were on a path in the complete opposite direction. Now with or without Marion, because of the financial flexibility, they have the opportunity to rebuild now, and compete again soon. (Before the trade was even official, Dan LeBatard* was already thinking about Elton Brand.)
The Heat should play out the rest of the season as if they just got their September call-ups. Give the minutes to the youngsters and see if Marcus Banks can at least be an upgrade from Chris Quinn and if Dorell Wright will continue to get better or if he's plateaued. The natural complement to this route is sitting the, if not gimpy, then certainly less explosive Wade. Sure, give him 15-20 games to play with Marion, to be able to assess their chemistry, but after that, considering he'll be playing on the Olympic team all through the summer, give him a rest.
Then they can go into the off-season with a healthy Wade, a lottery pick, a better sense of their youth and of Marion, and sufficient cap space to pursue free agents.
*LeBatard's upcoming article on the trade is due Sunday and is rumored to reveal that neither Riley nor Kerr initiated the talks.