I use predition book from time to time.

A huge issue of why I'm not using it more is that it's often hard to find interesting predictions to vote on. The Recent prediction page for example doesn't allow you to show a second page.

It doesn't seem to be possible to simply look at all the predictions on Tag X. I think the way stack-exchange works with tags functions quite well.

I think commenting should be separated from individual prediction making. There's no reason why the website shouldn't allow full threaded comments.