I think it's a lot better than WM2003. I haven't had any hard crashes or anything like that. It feels like a production release. All the software I've thrown at it, WM5 compatible programs, work great. I can turn WiFi and BT on and off WITHOUT having to soft reset! That was a HUGE annoyance before! The phone application works faster IMO. The one thing I can't figure out is how to connect GPRS without having to go to Network Connections. In WM2003 all I had to do was touch the "G" icon and from the bubble it gave me an option to connect. I use GPRS mainly for email and thankfully retrieving email automatically connects to GRPS by default. Of course there is still the ongoing BT problem where it shuts off when the phone goes to sleep. I didn't use my BT headset often anyways because I thought it was extrememly unreliable under WM2003 compared with my Wife's Motorola V551. That and BT softreset issue drove me nuts. I am extremely happy with WM2005. I was thinking about selling my SX66 until I decided to give WM2005 a shot.