Yes, MK was a madhouse on Friday 17th!! We live in Broward County, FL, and school was out for the county on that day only (teacher training, not a statewide holiday, or so we thought...). We chose this time for a long weekend in WDW precisely because school was out in our county, and did not expect to find the same was true for a bunch of other counties (we have used this strategy before and not hit this problem!). Live and learn!
We went back into MK on the Sunday and the difference was huge! At 2pm in the afternoon, the standby time for Space Mountain was 15 mins, and fastpasses were available for 2:35pm! The same was true for Buzz. It was an incredible contrast, and may have been partly because Sunday was a
MNSSHP night. It could also have been partly because the Food and Wine Festival had just opened - EPCOT was very quiet on Thursday evening when we arrived, but was a zoo on Saturday.
Having said all that, attendance is apparently up in WDW, and I am sure that Wishes, Mickey's Philharmagic, Mission Space etc are partially responsible.
Mike