Eclipse Working Set in 3.1M4

A cool new feature in Eclipse 3.1M4 is that you can organize projects by working sets.

I've got a lot of projects in my workspace which relates to different developments. My package explorer view is quite cluttered by dozens of fine-grained projects.
To improve readibility, I created different working sets (one for each related development) and I show them (Show > Working Sets).
When I focus on a particular development, I Go Into the specific working set and I only see the projects of this given working set.

Not groundbreaking but definitely useful.