I upgraded and it's a real sea-change compared to version 2 in terms of the interface. The GUI has been extensively tweaked and I'm finding it a bit confusing. Of course, I haven't really played with it much.
There are some indications on the jgsoft site that both EditPad Pro and PowerGrep are due for new versions soon as well, which is a bit ominious! AFAICT, if you buy v.X of a jgsoft app today and v.Y is released next week, you have to pay the upgrade (and I just bought EditPad Pro...). Of course, there is a line in the policy about reserving the right to waive the upgrade fee, so this might be done when the upgrade form is generated. However, the webpage for Regexgbuddy says that if you bought v.2 on June 12, 2007 you get the upgrade free, otherwise you have to pay (I bought v.2 over a year ago).