I've enjoyed both perspectives. We implemented last year and did see some issues. Things to watch out for:
Graphics Drivers (especially ATI cards)
Windchill cache (just use a new cache location)
Graphics Reps (we don't use them, but apparently caused crashes in at least earlier builds)
Later builds (m090+) do have lots of fixes (drawing cycling, losing tables, etc.)
Just a couple of notes on the system itself, though, I am one that dove in and have enjoyed the changes (well, with some exceptions such as the misstep on measure tool, etc.). There are some really nice pieces including the command search (oh how I wish other apps had that!), the Learning Connector (even if you don't pony up the $$$$$ for PTC U), tab customization (of course, the edits are by functionality, i.e. customizations have to occur to Part mode, Sheetmetal mode, Assembly mode, Detail mode, etc. are separate), Dynamic hatching, 3D dragger, etc.
The black eye, I think, for Creo Parametric is the interaction with PDMLink. It's astounding the issues that we (and many other companies?) see with the two flagship products not working well together. But we sigh and wish it could be better and just accept sub-optimal performance (and get beat up by our users).