At a previous employer we reviewed Accurev and Plastic SCM. At the end of the day, I was not impressed with Accurev's interface, or the so-called "streams". We went with Plastic, and nobody complained.
@Jonathan
The streams are interesting,but I don't see how any version control can magically avoid collisions when two people touch the same code in the same file. Accurev's model was intriguing, but at the end of the day, nice clean branching and merging with a drop dead easy interface made Plastic the choice for us. Plastic's timeline view (I forget the actual name), showing the branch/merge/check-in history made it very simple to review the history of the project from a bird's eye view.