The first round of the MLS semi-finals consists of a home and away aggregate goal system. The lowest seed hosts the first game and the highest seed hosts the second game. In my opinion, this does not give the advantage to the team that did the best during the regular season. At best the two teams are equal or a slight advantage is given to the lower seeded team. Here is why.
The lower seeded team can come out hard; early and usually get away with it. New England did this to us in 2004 by delivering some hard fouls early in the match to our playmakers and midfield anchors (notable was a Shalrie Joseph tackle on Simon Elliot, worthy of ejection but went without even a caution and Simon wasn't the same player after that tackle; Joseph did the same thing to Jaime Moreno when they played DC, btw).
Using home field advantage for the first game, the lower seeded team has more control over the flow of the game as the visiting (higher seeded) team must usually sit back and feel out. The home and away series somewhat turns into a two-half match (one half home and away). So if the home team can squeeze out a victory by a goal (or more) they still control the flow of the game because the second leg forces the higher seeded team to score that many goals plus one (to avoid penalty kicks). The higher seeded team will need to press for goals opening them up for counter attack goals. I think this format benefits the "boring", defensive teams that rely upon the two or three highly skilled players up top typically running a quick counter attack three on three or four.
The first round will feature Columbus vs. Kansas City and Chicago vs. New England in the east, Houston vs. New York and Chivas USA vs. Salk Lake in the west. If I were New York I'd come out full throttle for the full 90 minutes and rack up as many goals as possible on that crap Astroturf surface. I still think Houston will take that one in the long run otherwise. I would like to see Real Salt Lake get by Chivas USA just to give Jason Kreis a pat on the back for his years of service to MLS, give the fans a pat on the back for being patient and getting a new stadium, and to keep California out of the playoffs. In the east I think New England is too volatile and weakened to go up against a surging Chicago team. I also think the Crew will prevail against Kansas City but we might have to do so on home turf.