I agree, you don't want your chain too tight at all. Should be able to move up and down easily. It takes a lot for a chain to jump.

But I think chain tensioners are GREAT. I have built in ones on my Sputnik. When I am putting my rear wheel in, I just push it till it hits the screws and then bolt down. I know it will always be perfect tension on the chain and always be aligned. If you use a tensioner this way, it's great.