I just bought a Lumia 1020 for my girlfriend as she is big into photography. I've played a lot with it and am really impressed! I was a webOS devotee, and have dabbled with both Android and iOS and currently use an iPhone. And I have to say, that the Windows Phone interface is gorgeous. I love the use of whitespace, typography, and big pictures. App support isn't bad at all (with more coming around the corner), and I love the various app hubs (People app is very well done with Facebook integration). I could totally see myself making the switch myself soon, if it weren't for a few missing features. Many of which are real head-scratchers.
Can't save attachments from emails to the phone (this has got to be the strangest one of them all. I sent a video to my girlfriend and she can't even save it to share with her friends. She can view the attachment, but can't save it. And considering how the Windows Phone comes with Office and sort of touts itself as a phone that's solid at productivity, how can the fail to include the ability to save attachments, so you can edit them, and send them to someone else?)
Notification system is lacking. There's no central place for me to see my missed texts, emails, calls, etc. Sure I can check the lock screen or my homescreen, but that's just going to give me a count, unless I blow up the tiles (and that just shows the latest one). It'd be nice to have a central hub to really see the content and act on it accordingly. The notification system is antiquated (reminds me of something from iOS 3)
No way to quickly toggle vibrate. I have to dig deep into the settings menu. Same can be said for WiFi, Bluetooth, and the GDR3 rotation lock (about time this was added). Considering this was a huge complaint of iOS for the longest time, Microsoft had an opportunity to hear those complaints and include solutions to the limitations of its competitors in its own product. Fail.
API locked down. If Microsoft didn't restrict access to some much through its APIs, developers could really expand on the functionality of the phone including filling some of the gaps left by Microsoft. Seems like an opportunity to not only attract more developers but also generate more user interest towards WP8.
Other gripes are the fact that the search button is not contextual, meaning it isn't aware of the app you're running and open search for just it. And the volume is not separated for ringtone, system sounds, and media. And I just read that emails are threaded simply by matching the Subject field (so an email from someone 3 years ago that wrote 'hi' as the subject will be threaded with a new email with the same subject). That's just amateurish on the part of Microsoft.
But otherwise, it's a promising OS and one that I really want to see succeed.