I haven't played with it for eight or nine months, so my opinion may be outdated, but here it is, based on the demo version:
RPGX is a pretty application. It works fairly well for a core/RAW game and has a very nice interface and character printout. If that's what you're after, you'll probably like RPGX. Download the demo, if it's still available.
If you are someone with a lot of house rules, then it's probably not for you. I found it practically impossible to put in some of my house rules, like wholesale eliminating the Cleric class and adding a spontaneous Priest in its place. Weapon Groups from UA were right out, as was armor as DR (again, UA). My understanding is that it now handles psionics, but it didn't handle that or spell points when I was looking at it.
Edit: I just went out and checked the RPGX site. It looks like some of my issues with it (specifically, spell points/psionics) have been resolved or will be in the next release. I'll probably be downloading the demo again to check out the changes.