MLS teams don't come in to the USOC until the 3rd round. The tournament is usually set up regionally (to cut down on travel expenses/time), so I wouldn't think that those pairings will be determined or posted until the 2nd round is completed!

They are usually announced shortly after the 1st round is completed.

That way, teams will know who they are playing to play in the next round (make sense?)

Well, whaddya know...

http://www.ussoccer.com/articles/viewArticle.jsp_6782979.html

Well, I just found out that the bracket, as it is now, might not work out exactly how it looks. Meaning, the matchups in the quarterfinals could be rearranged and the bracket could get mixed up. (For example) Kansas City and New England (if they win their third round games, are certain that they will play each other in the next round.

Fourth round matchups from www.usopencup.com (why didn't I see this on www.ussoccer.com ?)

(New York Red Bulls / Crystal Palace Baltimore) at (New England Revolution / Richmond Kickers)

(Carolina Railhawks / Kansas City Wizards) vs (Seattle Sounders / Chivas USA)

(Chicago Fire / Cleveland City Stars) vs (DC United / Rochester Rhinos)

(Houston Dynamo / Charleston Battery) vs (FC Dallas / Miami FC)

The last three matchups each have three different hosting possibilities, depending on who wins the R3 matches.

Also, to speculate on the future format of this tournament...when MLS gets to 17 teams (assuming 16 USA teams), could they have the 16 teams enter into the second round? (The 32 lower-division sides play the first round; the 16 winners meet 16 MLS teams in the second.) I have been this as the future format for a while, and with the new compressed-schedule of the Open Cup, it would seem to free the MLS sides from the fixture-congestion problem.