The differences between CS5.x and CS6 are just outstanding. Adobe did not just do a few changes but redid their whole product line with updates. Photoshop, which I primarily use, has added into the software some amazing features that CS5 version couldn't offer without 3rd party intervention.
Adobe has a comparison list of CS5 to CS6. I had the links posted but Apple frowns on linking other pages in reviews.
If you haven't tried Photoshop before, this is great time to start. The creative technology that has been added in is a game shocker. I highly recommend this to anyone from beginner to advance users. I have been using Photoshop since version 3.0/4.0 approx 1995/1996. The overall logic has been the same, so the learning curve hasn't been overwhelming. The time you invest into this program will pay for itself later down the line.