OK, I installed Sharpreader today and ran it. I don't like that there's no way to mark a group of messages as read or unread. I don't like that it doesn't notify you when new messages arrive. These things have been said before.
I sort of like the way it groups related messages, but so far I haven't found this to be a killer feature, the way running inside of Outlook is (ala NewsGator). If NewsGator never develops this feature, I won't miss it a ton, as the temporal locality of related messages is currently high enough that I can remember what went on in a thread. Telling me about related posts in feeds I don't subscribe to would be way cooler.
The one thing about SharpReader that I really like is that it is insanely fast. Really really fast.
Anyway, you should try it out to see if you like it - it truly is a nice piece of software from what I've seen. Looking over my post from this morning, I see that it might seem that I was dismissive of it. That was not my intention: I want to say a hearty, "Well done!" to the author, Luke Hutteman.
Oh, and the issue with not running as non-Administrator is almost definitely that it wants to read from the program directory. Someone suggested that I just run it from some other directory (e.g. My Documents), but not only is that a horrible hack, but it still doesn't solve the problem of it not being multiuser. Still, it's an early version, and (I suspect) an easy fix.