If you end up with a web hosting company that sets a certain limit to giving/promising you certain load speeds (is that possible?) for your site, but you still see a ton of lag, can you get a credit of sorts? I am wondering what is going on with a site of a friends, we can not figure it out, but its really laggy.

I would assume that as with any business agreement, if you are promised something and do not get it, you have a right to a refund or credit. I've never really experienced it for myself, though.