If you can get a REAL deal (do some comparison shopping first) then don't pass it up, especially if you were in the market for a new computer in the first place. Be sure to watch out for hidden extras (why pay for speakers when you already have them) and salespeople trying to tack on stuff you don't need. I used to sell computers and believe me, we would push anything and everything at a person if they seemed willing to buy all of it.
I know, I'm rotten. Also, make sure it's not a system that's going to be obsolete in 6 months. If it's last year's model and they just want to get them out for new stock, go for it. If it's just for entertainment and a little school or work stuff I doubt you need the top of the line model anyway. My best advice is just to be well-informed about your purchase but it looks like you are already on top of that (with this thread).
