Good deal for both sides. Miami gets a bona fide third scorer and Minnesota gets an experienced veteran scorer (when he wants to) and a promising young player to add to their strong youth movement.
As of now, Minnesota;s young core includes Al Jefferson, Gerald Green, Corey Brewer, Randy Foye, Rashad McCants, Sebastian Telfair and now Wayne Simien, who was a solid player at Kansas and showed lots of promise his first two years in the NBA before being injured.
Say what you want about Telfair's maturity (or lack thereof), he will be a sparkplug in Minnesota if he gets it together, and with Foye and Brewer lighting it up out of the backcourt, this team can stay together for a long time. Don't be surprised if they contend for the Western Conference sometime in the next 2-3 years.
Miami, on the other hand, has a reliable fallback option should anything go wrong with Dwyane Wade's recovery from injury. Davis will complement Wade and Shaquille O'Neal nicely and can even take over in the unlikely event both are having an off night. Plus, Mark Blount is serviceable enough (something that Michael Doleac wasn't) and will allow Shaq to rest more often in games and keep him fresh.
Just an awesome trade.