Additionally, for those wanting to learn and polish your hacking skills, there's more 'individual' fun to be had in the Games - Sirens page. There, they have an ssh gateway, leading to 2 more servers, with everything from basic hacks to things like buffer overflows, etc. The Sirens games were evidently originally posted for a security mini-conference held for Novell's employees, a couple of years ago, and they have since made them available to the public. I've not taken the time to get through all of the exercises on there, yet (you'll see me on the scoreboard, about a 3rd of the way through the more advanced target box, at 130 points) but it's a good refresher.
Anyway, hope others find it both useful and enjoyable!
"All men can see these tactics whereby I conquer,
but what none can see is the strategy out of which victory is evolved."
- Sun Tzu, 'The Art of War'
OSCE, OSCP (Former - GPEN, C|EH - both expiring / expired)