They'll get to Aperture. You don't really need a Mac Pro if your primary app is Aperture. You might need one if your moneymaker is Photoshop.
I wouldn't even go that far to say Photoshop. Although it will utilize your systems video card, still not all the functions in PS do and the ones that do are still don't use it to the fullest. I would be more inclined to say a good iMac with a top of the line mobile video chipset.
Now what would use a Mac Pro to the fullest is say CAD programs like Solidworks, or software used for number crunching for SETI or Medical Platforms. And let me not forget the mass of the market for the new Mac Pro would be video editors without a doubt.
Then again, it depends on how patient the user is and if its a business were does productivity and development cost meet.
My personal stand point based on todays current Mac desktop models:
Mac Mini - Photography, Moderate graphics design and occasional video editing.
iMac - Commercial Photography, commercial graphics design, moderate video editing.
Mac Pro - Commercial Video Editing and Production, 3D Modeling/CAD and model simulation, Number Crunching for Medical and Stellar Research.
EDIT:
After posting this I realized. Apple doesn't have any "real" servers. They sell the Mac Mini as a server platform, but it isn't. Although it doesn't take much of a CPU these days to be a server, it lacks the ability to hot swap disk drives and it doesn't offer the data integrity(error bit checking)that a Xeon based server system would. This was a nich that the Mac Pro was covering. But no one wants dual video cards in a modern server. So were does apple go from here with a server platform. Could they offer a Xeon based Mini without disk drives allowing one to purchase a RAID system separately? Or could they sell a Mac Pro in the futures with a low end video card and internal Flash storage running in RAID mirroring?