I've been using Subversion 1.5 for a while now, and didn't know this existed: changelists. You can tag modified files so that you work on a handful of disjoint changes at once. When looking at your working directory status, the files are organized by changelist, and when committing, you can specify the changelist to commit.

This is the feature I missed most from Perforce, so I'm glad to see it in Subversion. I'm using distributed source control a little around the edges, but Subversion will be central at work, so it's good to have all the power I can.