Finding ideal belt tension (2 replies)

I've been really surprised to find so little discussion of belt tensioning in the reprap wiki and other resources. It's a huge issue in automotive maintenance, with tools dedicated just to it.

My question is, what is the ideal belt tension? What are some ways that you check if your belt is tensioned correctly? What are the pitfalls of over (and more obviously, under) tensioning belts?

Thanks! I hope this can be a resource to future rep-rappers.