I'm rather surprised I didn't see a thread about this type of mower here.
I got one for $5 recently and after a few adjustments and oiling it, It runs pretty well. I might sharpen it yet, Though.
I was using it on the day I posted this, And I think it's a great way to mow grass if you have a small yard and keep up with it. You can get exercise while doing it, It doesn't stink up the planet, It's quieter than gas mowers, It's a low-maintenance machine and it's also safer as far as kids are concerned (Though supervising is still recommended.) You can still get cut on it but if you see one in a yard sale, Why not buy it?