Sled Island is a lot of fun, but it's not like the typical festival. Because everything (other than Olympic Plaza) is at different venues peoples experiences really vary. From what I've seen it is populated primarily by the hipster/indie crowd and almost everybody is 18-30. There can be a major party vibe, or it can be mellow - depending which venues you head to. That said, everything during the day tends to be pretty laid-back. The day-time shows tend to be dominated by the smaller bands, weird venues and all-ages shows. The high school kids can get obnoxious at Olympic Plaza the way they tend to at Mac Hall (gossiping loudly at the front with their backs turned to the band), but as soon as someone comes on that gets the older crowd excited they get trampled and vanish. Lots of people are working throughout the week so they won't make it down until 7/8pm and might leave before the last band but enough of us will be partying through the night and stumbling into work hung over after 5hrs of sleep to keep things going until the end.
I've bought a wristband in the past, but I found that I don't really move around enough to justify the price - I'd rather risk missing a couple of bands I like then leave my friends to head elsewhere. Now I tend to just decide where I'm going to be each afternoon/evening and buy tickets for that and it comes out cheaper. Committing to one venue means you waste less time traveling between them and are introduced to a lot of new bands. For the nights I recommend the Legion - it's a fun venue, not too expensive, goes late, always has a good lineup and good crowds that are ready to party. As a bonus because it has the upstairs and downstairs there is always a show on so you don't waste your time waiting between sets. Central United is a good combo with the Legion because it is so close and has amazing acoustics - I tend to head here when I need a break from the energy of the Legion. It is also in the alley behind Central that you can find a lot of people blazing/drinking/smoking whatever.
“There is nowhere to go but everywhere, so just keep on rolling under the stars.”