The HD is nice, but other than that this upgrade is pretty weak. I really was hoping for at least builtin bluetooth. I have no idea why bluetooth isn't that big in Japan. I use it FAR more than WiFi on handhelds because it's battery friendly and with EDGE I get great download speeds.
Like a couple others said before, I think I'm just going to wait for HP to finally release a clamshell PPC. Hopefully it'll allow dual-boots (I think M$ crushed that ability with WinCE 3) since I'd rather use PPC to run most apps and to sync PIMs to my Mac. I'd want the dual-boot ability with Linux, though, so I can hack in the bash shell and mess around with some OSS apps.
If Nokia would ever fix their horrible Contacts application, support Perl/Python like the advertised months ago, and if iSync would support Nokia phones, I would also consider a Nokia 9500 or 9300.
Sharp looks like it's going the way of Sony... so my C760 will likely be my last Z. At least it's got a lot of life left in it and hopefully ROMs and apps will continue to get better over time.