Well... there are others on this forum.

I don't see that having them move up and down as a major problem, since it's the sideways movement that affects where the knee is pointed - it's where I'd link knee targets if I had them.
Actually, if I remember right you can limit different axies that the child inherits (so you can switch off vertical movement... It's been long time away from Max, but you'll find it in the hierachy tab)