I've been using Mach 3 razors for a number of years now. Actually, I have two of them. When the blade in the one I use to shave my face begins to seem dull (or draws blood) I put a new blade on it, and move the old blade to the other razor that I use exclusively for legs, arms, privates, etc.
Back when I first started shaving with razors I'd have probably cut myself to ribbons using such tactics, but the skin seems to adjust to such mistreatment over time, so basically I get good, close shaves - and good razor economy - with relatively little bloodshed. (really!)

I've thought about maybe upgrading my little system to a couple of four-or-maybe-five-bladed razors, but I can't help but wonder at what point the increase in the number of blades starts hitting the point of diminishing returns.