There were a couple sad UConn fans sitting in our section. (They were there on Friday as well.)
They were doing a lot of turning to the rest of the section and screaming 'UConn! UConn!!!' after every big play from the Huskies (to which the guy in front of me would yell 'What year did you graduate?!'

), so it was pretty funny to see them sitting there quiet and sad toward the end of reg and as OT wore down. However they actually did deal with shouts from Mason fans pretty well. They were youngish guys and I kind of thought they might resort to the typical 'Hey I'll kick your ass' crap but they just waved their arms in disgust mostly. Kept it fun. Anyway...
As a Terp fan I can imagine how crappy I'd feel if they had only to get past a team like Mason to make the Final Four and couldn't get it done. Crazy.
SD - I definitely fall in the 'cheering for GMU because I live in the area and wanted to see a cool upset' crowd. However I would have rooted for just about any team against UConn, as you have to pick a side to keep things interesting and more often than not it's more fun to go for the underdog.
To me it seemed like at least 2/3rds if not 3/4rths of the crowd was pulling for GMU. Now my section definitely had way more GMU fans than UConn fans so it's possible that skewed my perception here. The GMU official section was definitely more boistrous than UConn's. Weren't many UConn students that I could see (just a small section) whereas GMU had a full upper deck section packed with students.
I'd guess well over 50% of the people cheering for GMU hardly watch a game of theirs during the season (I don't unless they play the Terps) but there were quite a few GMU shirts/etc I saw walking around. I definiltely saw more GMU shirts/etc than UConn shirts.