Having just gone through the transition from CS3 to 4, after 2 months I don't look back. For me, there were two differences. The overall layout of the desktop, and the layers palate.
You can set up a custom desktop that is almost the same as CS3 and save it, so it loads when you start PS. That solved problem 1.
I've gotten used to the layers dialog. Since I find it slow, I've renamed a few custom keys. F2 = levels, F3 = curves, and F4 l= unsharp mask (which I still apply to layer masks even though that is now built in.) I'll occasionally use the new adjustments dialog, and it's only a bit slower. I think you'll learn it quickly, and it makes far more sense than keeping 2 versions.
Pul