There aren't many Windows Mobile 6.5 devices out there, but, we've had successes with ArcPad 8.0 SP4 and ArcPad 10.0 running on them.
The Windows Mobile 6.5 touch paradigm does influences the look and feel in ArcPad's UI by changing the placement and size of some of the buttons.
As to the crashes identified in previous post they were problems of ArcPad 8.0 SP2. Both ArcPad 8.0 SP4 and ArcPad 10.0 had improvements targeted a variety of memory and performance issues. The main concern was how ArcPad 8.0 SP2 performed on high resolution devices (thus causing greater memory usage) but were not connected to the fact that the OS was Windows Mobile 6.5.