I am currently on the look out for a Z, any of the 6000 or C3X00, and first of I didnt liked the clamshell design, so I thought that the 6000 would be good enugh, and if I were to mod in bluetooth, I would be having myself a nice little geek tool.
But then, when I realised how hard it would be to find a 6k for a decent price, and when I read up on the c3100 and the fact that the HDD is exchangable for a CF (and the fact that 4gb flash is cheaper than 4gb CF HDD - at least here in Sweden) I thought that hey, music goes on the HDD (which can be upgraded for 8gb or more further down the road) and sensitive data (school work, that kind of stuff) goes on a 1gb SD card, I thought that heck, battery time might be less but the keyboard is more indeed, and the weight difference is not that large between c1000 and c3x00 either...
Anyways, to make a long (obviously) story short, Im leaning towards a c3100 these days...