A week out from E3, the folks over at MMORPG.com were able to catch up with Principle Lead Game Designer of Star Wars: The Old Republic, George Zoeller, to talk about how the advanced classes will shape up.
Up to this point, the SWTOR devs have been releasing juicy video teasers on class progression, but not a great deal of information is available about how to attain advanced classes and what the skills will look like. Check out some of the highlights in this very extensive interview on advanced classes:

Zoeller also added:
At the same time, we’re taking care to retain the proper Star Wars feel and identity for each of the classes (e.g. a Trooper won’t get access to the jetpack/jetpack themed abilities the Bounty Hunter has and the Bounty Hunter won’t get access to Assault Cannon style weapons).
A lot of thought is also going into the design of the technology based classes to ensure they match the Force using classes in capability. Jedi are fearsome opponents, but certainly not immune to some well timed shots in the back from an Imperial Agent’s sniper rifle or the flames of a Bounty Hunter’s flamethrower.
Check out the full details of the interview here.