I have a Samsung Focus i917 as a test unit.
First off the hardware is great. The screen’s beautiful (AMOLED), battery life is typical, with only the memory card (perminant) pairing being the only issue.
The OS however feels lacking. Windows Phone works. There’s nothing wrong with it, hasn’t locked up on me nor had any major issues to point at. The real negatives is what the OS doesn’t have off the get go. No native msn messenger. No Remote Desktop Client. No SIP Dialer. For me, I have come from an Iphone where all those were possible. Upon research on implementing my own alternatives I found out the primary reason why nobody has bothered to release a proper messenger,RDP,SIP dialer, the os currently only provides http/https communication. no udp/tcp packets are possible for the applications to utilize. This seems consistent with what’s offered on the OS, facebooking,office,skydrive and emailing all likely done through HTTP/HTTPS (WebDAV). Youtube being the unconventional and offering only a mobile browser site that links to their streaming friendly video clips that likely runs off Windows Phone’s media player.
If you don’t ask alot out of your phone then windows phone fits the bill. I can see why MS took the stance of marketing the device as a glance and forget phone promoting people to minimize their time spent on the phone.