I saw some old friends here: Flickr, Library Thing, etc. After viewing some of the other categories, I can definitely say you've given us the best of the best.
I explored some new categories--Travel and Events. I was especially intrigued by the Travel category. Kayak, http://www.kayak.com/ put all discount travel sites together in one place--a real boon for comparison shopping. Travbuddy, www.travbuddy.com was a nice site for sharing travel experiences thru unbiased travel reviews. Tripmojo, www.tripmojo.com, did a real fine job of comparative pricing of hotels. The Wayfaring site, www.warfaring.com was beyond me.
I might suggest the Kayak site to someone who wanted to do comparisons. I'd personally use Tripmojo.
In the area of Events, I couldn't link to www.evnt.org The link was broken. www.Zvents.com brought up poor results. But I really liked Eventful, www.eventful.com I searched dog shows for the Bellevue area. It came up with some wonderful (and weird) competitions in the surrounding area, not just Bellevue. It also is a site I might use for event info.
The key here was ease of navigation and familiarity. I did check out the categories of Books and Personal Organization. Nothing can hold a candle to www.Librarything.com and I thought the Personal Organization sites didn't have much imagination. http://voo2do.com/ was the only one that looked even halfway inviting.