Very good -- we tried them while still warm, and they weren't as good then as they were the next day. We tried them 3 ways - plain, with cool whip, and with buttercream frosting from a can. Definitely liked them best with the frosting. It really added something to the peanut butter flavor. I have a very similar recipe I make without the peanut butter (but same cream cheese mixture) -- that recipe just calls for a 9x13 pan (I think you could easily convert this cupcake recipe to the pan and it would be just as good, if not better). Also, I swirled the pb mix into the brownies, but I would try piping it in like other reviewers mentioned -- it bakes up a little crusty when some shows on top.