Has anyone tried the new 1.8 snapshots yet? The addition of new blocks (granite and a couple of others) is pretty darned cool. Also, you can use your slimeballs to create a slime block - which bounces (and seriously slows down approaching mobs). The new rock types make caving a much more interesting experience (at least visually).
As for servers, I've never been on one - but it sounds like fun. I watch the Mindcrack vids on youtube, of course. Seems like a server works best when you can interact with lots of people.