What it seems to be is a place where you publish things (posts? articles? entries?) that other people can find in a variety of ways, comment on, and vote on. The main ways of finding posts seem to be through tags, the automated lists of most recommended and most viewed posts, and Gather's "editor's picks". There are at least a few other community features, including "connecting" (similar to friending on social networking sites such as Friendster and Tribe), and "Gather Points" which through commenting, having people vote for your posts, inviting people to Gather, and so on.
Points seem to be redeemable for... stuff of some sort. Probably not money, but maybe. Which ties in with some of what yaoobruni just wrote on his more respectable blog, about Web 2.0 and the web serf. Especially the parts about money mattering, users being excited even by small rewards, and the "company store" :-)
So, you can find my stuff at cos.gather.com - yes, I admit, one of the reasons I signed up was to grab "cos" while I still could.
Do any of you use Gather?