[ryanbrunner]

I think that's a fair point, and I wouldn't expect a video I watched 10 years ago to factor in very heavily on what I'm seeing today. But at least in my experience, it doesn't appear that the engine takes anything that happened more than a few days ago into account.

As an example: I watched a few episodes of Penn and Teller: Fool Us yesterday. I hadn't really watched it before, and while I like Penn and Teller in general, I don't remember watching them all that much on YouTube prior to yesterday (I'm sure at some point I had watched a video or two, but not more so than anything else I stumbled on.)

Today, 12 of the top 30 videos on my YouTube home page are specifically Penn and Teller: Fool Us. Not magic in general, not Penn and Teller in general, but specifically that show. That seems like the very recent past is way overrepresented.