Frankly, I had been using the Treo 750V with my 3G data plan for more than 8 months, but I'm not satisfied and won't recommend this phone to others, because it is not so stable and I asked for a replacement already. Also, I have to restart it at least once a day (I know I know, it's acceptable for most WM users out there).
Anyway, I just install Windows Mobile 6 on my Treo 750V successfully so I hope this would enhance my device and fix some bugs. Also, please also read this doc about the difference between WM5 and WM6.
I run into a problem that my laptop cannot wake up after sleep / hibernate, I try many different settings and combinations in power management of Vista and no luck, so I suspect it is related to my recent installation of KB939979 or KB938194?!