It hasn't been that long, but I can already barely remember a day before AO3. Archives are my great love in fandom, and it was a dark, dark period for me when everything was on LJ. I love wikis, and I think our legal activism is some of the most important work we do, but as a user, it's all about AO3 for me. I coveted Yuletide's matching system for years, and now it can be mine! No less exciting is the realization that AO3 is awesome for vids. It's easy to aggregate multiple types of hosting with search functions that favor fandom. As a mod, as a vidder, as a lazy person looking for something quick to read before bed, AO3 deserves my money, this year and every year.
Also, I want another one of those totes. They're totes awesome.