I use Pro-e on a daily basis. I also use Mastercam daily. Pro-Nc has it's pro's and con's as does Mastercam. Imho, I prefer to export to Mastercam and program from it. It's alot easier and quicker to get the simple things done. Where I work, we do alot of prototyping and I prefer not to have to deal with keeping the associativity between our designers and the upstream cad model. It does sound nice, in theory, that " yeah we changed the model....go ahead and update your nc file" but sometimes it's not as easy as it sounds depending on the changes made i.e. if they made serious changes to feature you used for references you be spending a whole lot of time re-routing things anyway. If your a very well versed Pro-E user this might not be to bad but can still get sticky at times. The whole learning curve of Pro and Pro-NC is a little steeper too, but on the design side it is well worth it and depending on your application, could be worth it onm the cam side. For what I do, I stick with Mastercam. It imports step, igs, dwg-dfx just fine. You can set up templates and libraries (as you can in Pro-nc too) and the latest version of Mastercam has "Change Recognition" that monitors your database (igs,step) for changes, shows you whats been changed and helps you update changes. I haven't used it much but it works. Like I said, just my opinion from my application view point and experiences.
