I dig it! I'm a big RoyalTS user, but this is great. Just to be able to sort is a major function that Remote Desktops lacked.
That being said, one thing (while neat) that I don't like is actively being able to interact with the thumbnails. I like the thumbnails being active, but in viewable only. That way, if I was to double click the thumbnail, it would open to the full screen, rather than having to double click the thumbnail "name bar" to open it to the full active screen.
I think it can be dangerous being able to click in the thumbnail, not really see what's happening depending on the size, and being able to accidentally perhaps change some random stupid display settings...or worse. Yes, the likelihood is minimal...but still possible.