I agree with adf, prices are dropping on Ebay and if my prophecy completes itself it should continue to bottom out through December 31. As long as no new major retailers get anymore 6k's and dump them into the market the price will begin to rise again somewhere around the 2nd or 3rd week in January and by Valentines day you won't see them going for less than $500 anywhere. I do wish that they would stay super low for as long as possible since not only can they be cheaply obtained, they are also driving the cost of 5x00's, and the C7x0's down a LOT! This can only be good for the Zaurus community as it enables hundreds of new people to cheaply become owners and also enables current Z owners to upgrade, (and then sell their old Z back onto the market bringing ever more ppl into the Zaurus Family!)
The bottom line however is this: The Sharp Zaurus SL-6000L is a great value at even $600! So there is no need to regret your purchase, or punish yourself simply because prices have dropped.
Enjoy your 6k and Merry Christmas!
-NeuroShock