Borderlands - Skilltrees Online

The Borderlands site has kicked up a skill calculator thingy for four characters.  Rock, Paper, Shotgun has an article on this, which also gives further background and information.  A snip with the links:

Here’s sneaky-lady Lilith , heavy-frenzied mouthbreather Brick, camping-bastard Mordecai and the hilariously inappropriately named Roland. And some further explanation follows…

Firstly, it’s worth noting this isn’t the whole of character development. You also have skills in individual weaponry, which increase through just use. Concentrate on a single weapon and you’ll increase its skill further, at the expense of flexibility. Secondly, there’s also quite a lot of equipment-based character specialization. As well as things like choosing weapons appropriate for your abilities, you get to plug in fancier ability sets which give you boosts in area. For example, increasing the amount of ammo of a certain gun sort you can carry. And extra slots for carrying weapons and equipment open up as you progress.