If you're waiting on purchasing a 360, you might want to wait a little longer. Say until fall, when the Xbox Falcons hit the market.
According to the San Jose Mercury News, the "Falcon" is the name for the xboxes with 65-nanometer chips instead of the 90-nanometer chips in current Xboxes.
Less nanometers means less cost for Microsoft (which is nice, but why would you care?) but it also means less heat. And that should mean more reliability.
And there's also the little matter of the HDMI port. According to San Jose Mercury News, Xboxes with HDMI ports don't necessarily have the 65nm chips within. Especially the first runs of Xbox Elite machines. Overall, it's a little bit of a crap shoot, as Microsoft has no intention of telling anyone which chips are in which machine.
So, theoretically, the longer you wait to pick up an Xbox, the better chance of having the new chips. Hope this helps.