I did do several upgrade through PowerMax. The first I traded my nearly 8 mo old G3/400 (with 512mb RAM) for a G4/400. Given that I was desparate for the latest machine I got $800 for a my new G3/400 (which I paid $2500 the 8 months before) and had my new G4/400. The experience was great, did I mind losing a machine for only $800, no.
Later I called in to get a quote on what I'd get for my Lombard machine that had 192mb RAM and the 6 gig HD, (with was the low end model, 333mhz, which I got at the same time as my G3/400 tower) the said for my machine I'd get $1700! (paid $2500) that was a Friday, I should have followed up then. I called Wednesday of the next week and because Apple was about to announce a new PowerBook (the Pismo) they had to lower the price to $1300!
Anyway, I had an extra 3400 and I pretty much paid only $300 for the high end Pismo.
Because I can't afford to lose anymore money with a trade up, I'd rather buy and keep (or sell through ebay and get more out of selling than trading) my "old" computers. But if I had to trade up, I'd call PowerMax right away!
Plus you don't pay taxes and shipping isn't that expensive with PowerMax! AND you can also BTO items through PowerMax (who then BTO's to Apple) but DOES not charge taxes!