I had a GPD Pocket at launch and used it for a long time - it went everywhere with me. Traded it a couple years ago and I still regret it.
Presently I've got a Sony VAIO VGN-UX72 that I've been hunting a working battery for. Installed XP on it, as it's 1gig isn't very Vista-friendly, and got all the original XP VAIO software and drivers working perfectly. What a little bundle of joy, I wish I could send it back in time to my younger self who was salivating over the UX and OQO devices. Kinda surprised at just how much performance can be squeezed out of it. Playing Typing of the Dead on a thumb keyboard is a special experience.
I've also got a Sony VGN-U50 with dock and keyboard that I've gotten to power on twice for short periods, the stock battery seems to charge and the aftermarket battery I bought does not. Can't figure out why it boots sometimes and other times not. Mostly it just flashes it's backlights at my when I try to boot it. If anyone has experience debugging with one of these I'd love some tips.
Presently I'm still hunting down more Sony and VAIO pieces and waiting for something as compelling as the GPD Pocket to release with more power. I'd love if a gaming handheld style UMPC like most modern GPD offerings or the Steam Deck would have a nice dpad and a sliding display with a thumb keyboard. GPD Win 3 came close by copping the UX design but it just seems like the build quality isn't there.