By the time you pay tax, it's like $50 more to order a new one from macmall.. I bought one refurb - a TiBook, it was such a POS, I'll never buy refurb again. At least with properly used, you get a real break on the price.
From personal experience, and from many forum members, Apple's refurbs are very good quality. In fact, because of the scrutiny of their inspection, many feel they are superior to new. Also, sometimes it just feels better to order directly from Apple. (I posted before I read the above post)
As for MacMall, I have heard a number of stories of late deliveries, rude salesmen, and charging your credit card multiple times.
If you feel that MacMall is a good reseller, so be it. The point of this thread was to alert those who have been wanting an Apple mba refurb; often, they appear for a short time and are missed.