I generally try not to; my Current will talk about girls he's dated, but it's not a big deal, and he said he doesn't mind if I talk about mine. However, I told him I wanted him to be reacting to me and not to my ex when he was with me (ie not trying to not be the things about my ex I hated), so I said I didn't want to talk much about my ex. When my Current hangs around with my friends, it will sometimes come up (it's a female-dominated group and we indulge in the occasional rant), but I have yet to really get into the specifics of what went wrong. I'm guessing I'll tell him more eventually. Actually, I told him when I was concerned/pissed about being "monitored," but it was more like "this is why I am in a bad mood and kinda looking over my shoulder a lot" than anything else, as I had just found out about a small part of it.
I'm sort of going for the slow reveal, I guess, on Ex1 and on some of the other crappy parts of my past (on the same react-to-me-not-my-past principle- which I also explained), though I did tell him awhile back that if he had any questions he wanted to ask, at this point I was OK with telling him, and I have told him a fair bit about my family.