I've never been on the actual weekend before, but we were there the Friday after Memorial Day last year and MK in the afternoon was much more crowded than what I'm used to (2 out of our 3 trips prior to that had been during the awesome crowd void that is the week before Labor Day). I've been to EPCOT, DHS, and AK when it was crowded, but personally, I'm the most sensitive to crowding at MK. I think it's because there are relatively few attractions that I stand in line for at the other parks. At MK, small changes in the length of lines can really throw a wrench in your plans. If I do a dozen rides and it takes me 10 minutes longer at each ride than I anticipate, that's two hours or extra touring time needed. Also, Main Street USA can be a huge bottleneck, especially at parade time. For what it's worth, here's a quick mini trip report from last year's Friday after Memorial Day in MK:
We were 5 adults (co-workers) using conference tickets, so we couldn't get into MK until 2pm. We got delayed a bit and actually got to TTC a little after 2. We were staying offsite, so when we parked at TTC, our first half hour was eaten up by parking, monorailing, getting our tickets from will call, etc. We hit Fantasyland right around 3:00 and we toured until about 8:00 when we stopped for dinner and proceeded to the parade.
We did Under the Sea (FP), It's a Small World, Stitch's Great Escape, Space Mountain/Carousel of Progress (we split up), Big Thunder Mountain, Met Mickey in Town Square, did some shopping and ate dinner at Cosmic Ray's. I feel like we might have squeezed in Haunted Mansion, but I can't remember for sure. Our touring pace was leisurely and we able to utilize fast pass for Under the Sea, but we had to do standby standby everywhere else. That took us about 5 1/2 hours and we watched MSEP before hopping the Monorail to Poly for Wishes & dole whips.
Part of our limited riding was because it was crowded and lines were substantial (30 minutes plus for most attractions), but also because the one lady that we took was a 64-year-old Russian on her first trip to Disney and taking her to It's a Small World and to meet Mickey at Town Square were top priorities. Getting to watch her experience those two things was some of the best Disney magic I've ever seen! Another member of our party really wanted some time to shop, so that changed our ability to hit more attractions, too. As we got into the evening, fast pass was also not available or convenient for many attractions.
We did a lot of back tracking because we didn't really do a lot of pre-planning. We were in town for a conference and I couldn't pin our boss down about car rental and other logistical issues until about a week before the trip, so it was a last minute decision to get the tickets and most people couldn't tell me what they wanted to do ahead of time because they had never been before. I felt like we hardly did anything because I am all about rope drop and I could have knocked out those rides in two hours on a normal morning, but my friends who didn't know any better had a great time.
The usual wisdom still applies: be at rope drop, prioritize the things you can't miss and get FP's, pack your patience and enjoy where the day takes you. You're going to hit the 24-hour thing of you're only going to be there Friday and Saturday, so it will probably be crazy, but I think I heard that EPCOT and DHS will be open 24 hrs. also? Can someone confirm? Because that should help tremendously with the crowds at MK!
We're there Friday/Saturday which is better than Sunday but I'm curious what a 6-7 kind of day is like. We plan on going early each day to try to fit some time in before crowds get wild, but I'm wondering if we're taking a big risk by doing two parks. 
