I've now spent the best part of an afternoon trying version 2.0 out. My verdict: Stick with 1.8x. Regardless of the claim that it was 'rebuilt from the ground up', perhaps they should have stuck with what worked. My main gripes are:
* ALL caches wiped without question, no attempt to migrate. If you have a large library of headers, they will be wiped.
* Favorites aren't imported. All you'll see are NULL folders.
* You can't mark files as read, only messages. No matter what you do, you are working with all the headers in a particular group. This means that if you have a group with 7.5 million headers (like I have), they are parsed in any and all searches. You cannot just work with unread stuff here.
* You cannot focus on messages in one group or files in another. The selection you make at the bottom of the screen is global, and you have to remember to switch back and forth depending on whether it's a file or message group.
* If you have many headers, like me, it's dog slooooow. Headbangingly, beach-balling slow.

So, should you buy it? Definitely not. It looks like the developers really think that UI stuff is everything, while back-end effectiveness is a byproduct.

I'm disappointed in Panic--especially given the time it took to get an update. Mac users effectively don't have a good newsreader anymore.