plasma - 1:10 pm on Jan 10, 2007 (gmt 0)
I read somewhere that .org and .net domains can be pretty expensive in the future, as the price might be adjusted - even after owning the domain - to anything that the registrar thinks it's worth.
I personally never consciously visitted (or linked to) a .biz site. They somehow sound like "too late" or "me2".
Better stick to country domains, if your content audience is mainly from a certain region, or .com if it's a global ecom site.