"what negatives have you come across after having used them for a while?"
I, like some of the others, have a Compaq R3000z, which is Compaqs version of the zv5000z.
As mmoy notes, the drives could be better. I swapped mine for a 5400 rpm Toshiba, that solved my problem. Other than that, the power connector comes unplugged pretty easily. Linux installed pretty easily, but there is a lot of modifying several config files to get everything operational. The touchpad can be a little dodgy, I use an USB mouse. When gaming, sometimes a key "sticks". That can be exciting when playing a shooter. That seems to be a keyboard thing, it happens under both XP and Linux. And yes, I have StickyKeys turned off...
I got my unit pretty stripped down, I splurged on the A64 3000+, GeForce 440, 802.11 and the 12 cell battery. With 256 meg. of additional RAM, the hard drive and a 2.5" IDE to USB converter so I can use the original drive as an external, I paid right at $1100 total. I certainly recommend it...