I used to keep mine private, but I made it public. I also made my subscriptions public. I don't have anything I'd consider weird in it, and I think it helps show that I interact with YouTube instead of just posting stuff for views. Maybe YouTube will ding me for sending people off to another channel, but if they click on a liked video of mine, they would be watching the video inside one of my channel's playlists. I suspect that because it's one of my playlists, it might still count for something...and at least it's keeping nosy curious people on the site longer, and a lot of my liked videos are somewhat related to my own channel. ^_^
I think there are trade-offs, but I don't think there is a clear negative to it unless you've liked a lot of controversial or strange videos... It does make me think twice about liking a video, though, which might be a good thing.