Here it is the middle of August and a new Mac Pro has not been forthcoming. As I discussed back in June, there is not a lot that could be done right now. And as I predicted— it does not make sense in a technical or business context.
The current Mac Pro continues to make sense for any professional with work to get done, especially as an MPG Pro Workstation; there are no "missing pieces" to worry about and the Mac Pro is a proven rock-solid platform.
I continue to favor the 3.33 GHz 6-core Mac Pro for anyone with robust computing needs, but the 2.8 GHz or 3.2 GHz 4-core models are also excellent choices, with modest performance differences for many tasks. Serious video users are best served with a 12-core model.