I just switched from Verizon and my Treo 700w to ATT and a BlackJack II.  That also means I am moving from Windows Mobile 5 to Windows Mobile 6.  Thoughts so far?  It is a much snappier device, that is for sure.  I miss having a touch screen interface, but mostly when I am browsing the web.  The biggest thing I miss is that the Treo would try and anticipate text recipients and words when I typed text messages.  No such feature in the BlackJack.  The BlackJack II does come with a pre-installed RSS reader and that has been a great addition.  I also was able to enable the GPS feature and it works great with the Live Mobile search app.  The only other thing I miss from the Treo is you could add Speed Dial entries directly to the home screen.  I haven't found a way to do that on the BlackJack II - it could be because that was a touch-specific feature on the Treo, but it would be nice to be able to scroll through pictures of the people you usually call based on your contact list.  But the perf and nice screen seem to balance out the missing features - so all in all things are going well.