I've just played around with it a little bit and I don't think I like it either.
If I narrow down my view to a subset of my data and then want to do a quick search in that, or filter some additional stuff out, I no longer can. As soon as I start typing, MC decides to reset my view to All.
Sometimes I may want that behavior. Most times, I don't. Before this change, I could get that same result if I wanted, by simply selecting All and then doing my search. Now, there's no way I can do a search within the data I've drilled down to.
And worse, if I do the search first, and then try to filter that further by selecting something in the panes, MC resets everything again. Now, if I only wanted to select the one item, it's ok. But what if I wanted multiple items?
For instance... let's say I want to play every song featuring Metallica. I can type "Metallica" in the Search Box and see all of my Metallica albums, plus a few songs that they appeared on along with other bands (eg. Trans-Siberian Orchestra feat. Metallica). Let's say that now that I've got this, I decide I don't want to listen to St. Anger (would anyone?). I can no longer easily select all of the items that contain Metallica except for St. Anger. As soon as I select something in the Panes, everything resets and my search is wiped out. The only way to do what I want is to manually select each file I want and make sure I don't include the ones in St. Anger.
Actually, the more I think about this, the more I hate it.