That could be tested, by placing a mark on the paper at 30 inches (or wherever) before printing, then measuring to the mark after printing.
Aside from shrinking images, how do you like the 2400?
I'm pretty sure the paper isn't shrinking but I'll try that next time, just to be sure.
As far as the printer goes, it produces the best images of any inkjet I have ever owned, and I am partial to the rag papers, as the mat saturation I can create is a wonderful look for certain color images. It's nice to not have to depend on a lab for some of my color images, and unfortunatly I'm getting better results by doing it myself, enough so that I am considering a 9800. I'm less partial to "photo paper" and really tend to like it as its own thing, with its own look, rather than pretending I'm making a silver print when I'm printing black and white. I think I will always prefer contact prints and large format enlargements for b&w.
Those are pretty much issues of personal taste, however, and don't reflect negatively on the printer, which is the best I've personally owned.
Aside from the undersizing (which I can deal with) I would say that my biggest "beef" with the printer is the tiny ink tanks, as it seems I'm constantly needing to change a cartridge. That could be solved, of course, by upgrading to a larger printer. I'm not aware of anybody who makes a bulk feed system for the 2400 at this time, but I would be interested if somebody did.