Close button sends client to the tray, statically linked Qt for OSX.
See the Changelog for list of features and fixes currently only available in the nightly builds.
The things I like/dislike feature was a very contested, not much liked feature in the original client. I've never ruled out implementing it in SoulseekQt, and I still don't. I wanted to see if anyone was going to bring it up, and you're the first one to do so actually. As a more dynamic alternative, I've implemented search correlations in SoulseekQt. Not only do you not have to explicitly list what you're interested in, but you'll get recommendations based on things you're actively searching for. Anyway, if there's enough of an interest in the original system of recommendations, I'll certainly consider implementing it.
Just a thought: for those who don't search much, the search correlations might not be very effective. I do find it a smart idea though!