My initial thoughts:
Firstly, as I said, I love the interface. It is incredibly clean, unobtrusive and easy to use (although perhaps because it is so easy to understand, the intro on gmail was a bit of a pain). Only other thing in general is my limit on recommendations for the service.
Product-wise, I see myself using this mainly as a way to stay in touch with business connections and see if they can use where they are/any new information to deepen our relationship or use their new position/status whatever to help me. With that in mind I really care about all my LinkedIN connections, some of my twitter connections and few of my Facebook connections. I wish there was a way for me to edit the feeds of whom I'm looking at and what I'm looking at beyond just 'favorites'(I don't particulary care about my high-school acquantances birthday...or to be blunt my high-school acquantance at all) and all this different information is kind of obscuring the important information I want to look at.
I know mingly catches when people on LinkedIN change jobs, but it doesn't seem to catch when they just change their headers, which some of my connections seem to be doing instead of properly editing their LinkedIN page.
Also, I know you guys are probably adding a lot of features, but it'd be great if there was a way I could follow a company or industry and be notified when one of my connections becomes involved with it.
Once again I really like Mingly and am looking forward to using it for a long time!