John's advise is good advise but if you do decide to play...
Installing the beta won't affect your 2.x installation but double-clicking any catalog file will try to open in Beta 3.
If you have files in 3 that you then want to move to 2 with your adjustments, select the files and press Cmd (or Ctl on Windows) +s to save an xmp file of your changes. Keep in mind that some adjustments in 3 probably won't directly translate to 2 but you'll be "OK". Then you can import into 2 with adjustments, ratings, etc intact.
I like 3. It's a little rough right now but it's pretty good.