My inexpert view of David Beckham's move to the Los Angeles Galaxy is that it's a great deal for Beckham and the beginning of the end for the MLS. Beckham will be able to further promote himself and, by extension, his wife, who I believe is a marketing/promotions genius. He has some name recognition in the US now, but that could go much higher if Mr. & Mrs. Beckham play their cards right. (And, I believe they will). The $250m contract Beckham signed with the Galaxy is already a great deal, but I think the Beckhams will do better than that.
As for the MLS - Beckham's not good enough to single-handedly lift the league. He's not Wayne Gretzky or Michael Jordan. I mean, this will be the first time he's been the best player on his team (even that I really don't know for sure), right? So, his name (known more from Bend it Like Beckham than anything else) will help raise the league's profile, but he's not going to provide loads of highlights and big headlines.
Listening to Football Focus today and reading what Arsene Wenger had to say, it seems that people over here expect Beckham to be only the first in a list of high-priced, big-name stars to go to the MLS. The big egos & salaries and fading abilities of those who do go will generate trouble within the squads and almost certainly not generate sufficient revenues to meet the salaries.
Hasn't professional soccer in the US already gone down this route when Pele, Beckenbauer, Cruyff and others played in the NASL? This doesn't sound like positive news for the league. I suppose the league is gambling that the millions of kids who've played soccer over the past 20 years or so will now, as adults, pay to see some of the biggest stars in the world. We'll see.