I'm not sure about Mark's question, but I believe that the 3-year HP plan starts when the warranty ends. When my partner bought his Z3100, the dealer told him that he could add the extended warranty later.
I have decided to order a 24" Z3100 (today, I recon), but I haven't decided if from my local Global Imaging or online. Edit: I guess Global did send a tech to help my buddy after a couple weeks of squeaking. The price delta is a $200-$400 depending.
I notice that NewEgg offers 3-year extended plan for $340 thru an outfit called Service Net that starts when the warranty ends, but it has a $1k per call and $2k per year coverage cap - for these complex printers, that's limited coverage.
In my purchase decision, I used the test image, "Lab_Test_Page.tif" discussed elsewhere in this forum. I obtained prints of this image on several different papers with the Z3100 and 4800. Both showed idiosyncrasies; should I post the findings of a newbie?