I don't have any experience with VW translation, but I have some in other CAD systems, like SolidEdge (UG product), Unigraphics, I-DEAS, and ProE. Here's what I know:
-STEP works reasonably well, but not all features are editable once you do the translation. However, you generally can shade and unshade the model. I don't know whether VW has STEP translation or not; I suspect not--most of the high-end CAD packages only have it as an add-on module for a hefty multi-thousand dollar price tag.
-Wireframe translators (I think this includes ACIS, but I'm not sure), generally don't work very well, at least for solid models. You either get just a picture or snapshot of the model, or you simply get a bunch of lines, arcs, and circles (primitives) that you can't shade or create hidden line views with.
-As far as Pro/E is concerned, I would love to see it on Mac OSX--that's a match made in heaven, IMHO. And, the way I see it, Pro/E and VW do not compete with each other--Pro/E is the best high-end CAD system available for mechanical and electrical design, but at a very high price tag (>$10K).
-VW, OTOH, is a very good low-to-midrange CAD system with a price you can't beat--it's an excellent buy at <$1K. Nemetschek/Diehl has done a very good job of adding real functionality with each new version while keeping the price low. I wasn't really considering upgrading to VW 9 from VW 8.5 until I saw that associative dimensioning and (limited) parametric relations has been added; these functions have traditionally only been available on the most expensive CAD packages. Yes, it may be available on AutoCAD, but it's probably at a very unreasonable price. I've always viewed AutoCAD as an overpriced low-end CAD system with a bad interface.
If I'm not mistaken, Nemetschek hired a former Parametric Technology manager to come in and help add high-end functionality to VW. It may be that the associative dimensioning and parametric modeling are the result of that hire.
Hope this helps.
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Michael B. Moore