Sounds like my first impressions are similar to everyone else:
My TrueHD test video doesn't stream TrueHD, but DTS MA works fine.
Indexing, scanning, and identifying is *slow*. There's no way you'd want to have to go through this every time you turn the box on. Full power down when not in use to conserve energy is just not an option until this data is stored locally. This is particularly true since Boxee chokes on higher bitrate movies while scanning.
I've found the operation of the "Back" button extremely frustrating. Sometimes it goes back to your last page... sometimes it brings up the drop-down menu... and it will never take you back to the home screen even if that was your last page. For example, move around the pages of the weather app, then try to get back to your Home screen. Have fun with that.
I hate that Movies go to only online movies, while local movies (and music/photos for that matter) are hidden under Files. I'd like to put Music, Photos, and Local Movies up on the home screen, and I'd readily trade away streamed movies to get it. Maybe that'll change if it integrates with Netflix/Vudu, but for now having Movies on the home screen is a waste.
I won't go into the positives because they've been covered in depth. I haven't had any of the file format issues you guys have, it's done quite well. I'm overall happy, but there's a huge amount of room for improvement, especially with the UI. I miss the beta UI.