I've been working with the pressure sensor again. I finally got a very ugly prototype of a hand-held meter built. The basic idea is that I have the pressure sensor wired to one of the analog inputs of an arduino, and then the arduino sends sample data out via serial to my PC.
I got some pretty good readings that look like I'll have a resolution of around 0.005 SG (which is usable, I think). The only major problem I ran into was that air was slowly leaking out the tubes that were in the water, which means the seal I have between the tubes and the pressure sensor ports isn't good enough. So the next thing on my list is to come up with a way to seal the tubes better.
Here are some pictures of the prototype: