BioWare has updated the official Star Wars: The Old Republic website with a new area called Game Systems.
The first entry deals with the Advanced Class System.
One of the examples on how the ACS works is the Smuggler Class - you know, like Han Solo, the guy most boys wanted to be when they grew up.
Smugglers are "lucky, opportunistic swindlers", but in the game you can tailor the class to fit your play style.
You can be more roguish by slipping into battle and quickly dealing with enemies before they can react - or you can add more of a ranger element to the Smuggler, by standing back and dealing ranged damage - or you can go full-on tank mode and just charge into battle like Rambo without a jock strap.
There's a lovely chart through here that explains it a bit more, and provides you with an idea of how the different customizations will be laid out.
SWTOR is expected sometime during spring 2011.
Be sure to also check out our latest interview with the game's executive producer at Lucasarts, Jake Neri while you're at it.