Since getting onto the Windows Phone 7 band wagon a couple of months ago I've been mostly impressed with the platform. Its still far from ready to take on the strengths of Android or Apple; and its lacking features that Symbian packs (although you'd be extremely foolish to choose the latter over WP7).
In terms of pretty much every important functional requirement my HD7 lags behind the Dell Streak. Data entry, multi tasking, screen size, route navigation, copy and paste, etc., etc.
So I'm more than a little surprised to report that that HD7 is the phone I most often grab on the way out of the door. Or even if I know that I need the functions of the Streak I'll find room to carry the HD7 too.
Part of the reason for that is the integration of Zune and my Zune pass. My HD7 is loaded with the music I want to listen to now. But if I want to listen to something whilst out I can get it without trouble our cost. Last night the children were asking for Christmas songs and I was without any suitable CDs for them. Two minutes of searching and downloading on Zune soon sorted that out.
Apple have traded on convenience with the iPhone, but this is definitely an area where Microsoft has them beat all ends up!