I just got one last week (Friday as well), and I can tell you that my Blackjack II is on eBay as we speak. When I'm no longer working in my current job, the Treo 750 is going on eBay as well.
It feels very solid in my hand, although I wish it had soft touch paint like the Treo 750. I was not impressed with the build quality of the BJII (it squeaked when I typed), but I liked it's battery length and phone clarity/bluetooth signal strength. Luckily the Epix kept the battery length and bluetooth, and got rid of the "cheap" feel.
I'm surprised just how much I like the finger mouse. I thought I would hate it, and keep turning it off every now and then - but it's like having a one-handed stylus. It's awesome! I did turn the speed on it all the way up, so it responded a bit better. The screen doesn't respond as well to screen taps as the Treo 750 does, and I absolutely HATE the haptic feedback crap. I turned it off already. I only pull the stylus out when I feel like it (and with SkyBook for Facebook - it doesn't like the finger mouse AT ALL), which turns out to be not very often.
This thing is FAST compared to both the BJII and the Treo 750. This is what WM is supposed to be! The WiFi and GPS are both working well, and the good news is that the GPS works with Google Maps and Live Search (although I did have to switch the Live Search to look for it on COM 9). I do like WM 6.1, but there are some things about it that I don't know if it's Epix specific or WM 6.1 (like there's no notification for unknown callers). The minor gripes I have thusfar are just that, minor.
There's a CRAP TON of AT&T bloatware. More than on any other phone I've seen. I deleted it all quick, fast and in a hurry. Didn't need it. I've installed all the typical programs I use:
SPB Phone Suite (needed to get the Beta version 1.3.1 I believe for it to work)
Wisbar Lite (for some reason with cascading menus, it adds a bar of white nothingness at the bottom)
WeatherPanel
Google Maps
Live Search
Windows Live (for push email)
Live Mesh Client
MemMaid
PMClean
PHM RegEdit
ScreenCapture
SkyBook
The only piece of software that I'm not stoked I had to install harkened back to my Treo 650 days: PDANet. AT&T's got this thing locked down, just like the BJII (not like the Treo 750) so no Internet Sharing. PDANet sidesteps that for me.
Hope this helps, and if you've got any specific questions I'll try to answer.