I had no problems upgrading from 2.6 to 3.0 for a mere 9.95$ US. the new serial is shorter then the previous one. the new interface is pretty clean. There is now an info on the opening screen that 4450 MB is the optimal size. this can be useful if you modify the desired size of the finished DVD.
I have used version 2.6 for many months now and I am impressed. Popcorn 1 is far behind except for creating DVD which do not need compression. Take a few minutes to read the documentation, as this could save you some time.