I noticed in the Canon S50 review a reference to an older article about using the similar Canon S30 as a light meter for large format photography.
I also have an S30 for visualizing my shots and getting light information, but I find one drawback of the S30, and perhaps the S50, that renders it a bit awkward as a light meter: it has limited aperture range.
It has f/2.8 to f/8 aperture in 1/3-stop increments. Since the minimum aperture is f/8, if you shoot typically in the f/16 to f/64 range you'll be doing some exposure shift calculations to get to the correct settings for the lens.
I mention this as the only real limitation this camera has.
Also, get a small jewlers Phillips screwdriver and regularly tighten all those small screws on the body. The S30 has 12, and I've had 4 of them fall out (two I later found in my pockets). Clear fingernail polish should help secure them. My metal S30 has some dents, and the unprotected rear viewscreen has become quite scratched, but I still love it and carry it it all the time.
It's nice to have a "cheap" means of recording shots, cheaper than 4x5 film. Setting up a 4x5 shot takes some time, and at a dollar a shot, 4x5 is not for snaps. But having a digital along is great, when I see something that might or might not turn out, or when I see a shot I'd like on the website but not one I'd ever put on the wall.
So my S30 is a member of my 'electronic quintet', the electronic devices that are always found in my vest when I set out on a large-format hike: light meter, GPS, digicam, PocketPC, and ham radio.