Trying to write today, as tomorrow my membership expires.
I've been using UG v.18 for five months now (after Pro/E), and I must say that I'm disappointed in it. I don't use anything fancy like complex surfacing, only solid modeling, sheet metal and drafting, but I think for these, UG is like more than 3 years behind Pro/E.
Examples: in SM, if you modify anything in your part you have to unform and form it back in order to update the model- which is a pain if you have a large assy with this part as a component- error messages (from mating conditions that don't conform anymore until you update the part, moved components if those are not fully constrained , etc.)
The flat pattern in UG is made up from a set of curves created and processed from the parent surface which are theoretically associative, but not quite always. It happened when I moved a hole like 1/8, the majority of these curves lost their associativity= the dimensions on the drawing lost theirs, too. Lots of fun when you have about 80 dimensions on that flat pattern to re-do.
You cannot create intermediate part states in SM- when you want to show part after the first bend, for ex.
The dimensions cannot be shown in the drawing (unless there are sketches or holes)- you have to create them like in AutoCAD.
Of course you cannot switch dim. to another view.
Creating and modifying dimensions is not as easy as in Pro/E. If you want to move one- select the dim icon, select the dim and move it, cancel window. Three steps vs. one in Pro/E. Same for deleting. Having lots of icons has been seen as an atu to UG, but clicking on an icon opens a window, than another... and so on.
There are other former Pro/E users in my company with much more UG experience than me, but none of them like UG. I know my opinion is biased due to the lack of enough experience in UG, but the (only!) few things I exposed here are basic. UG is based on, I would say, outdated kernel (uses parasolids, primitives) and don't see how they can make up for the gap going on the same path. They have developed Solid Edge, which tries to combine more of the two worlds, but is still a long way.
Plus UG is sensitively more expensive than Pro/E, and it lacks proper support.
(My) Conclusion: As of today, I wouldn't buy $5 worth of EDS (GM) stock. Maybe (and hopefuly for UG users including me) things will change.