Why use the proprietary PSD format? TIF is open format, lossless too, and has about the same size. I have to admit I use zipped TIF (which is more compact). For photos, why should you save layers? The flat TIF is enough, unless you do illustrations.
I save: the original CR2, the untweaked JPG from cam, and the final TIF with all the edits. From there I can generate the JPGs for upload. I save on external disks, at least 2 copies. On average, I obtain 30 Gig per month like that, that's one extra 1TB disk per year. Considering the price of disks, that's peanuts.