Honestly, pretty much if they're left alone for more than 5 seconds.

Yeah, that sounds about right. I still haven't reinstalled it after the FT update because I'm rather enjoying keeping control of things. I might put it back in once I finish up my current legacy story (hey, you can really only work a one-child handicap if your sims are trying for a kid every ten minutes) just for my self sim and her hubby. The day I was uninstalling the objects for my FT install, the two of them headed for a bed seconds after I removed it from the lot. Hell, part of the reason I hooked them up was because they hooked up on their own... and apparently tried for baby on a community lot all on their own. Hell, until then, I didn't even know you could Try for Baby in a hot tub.

Hmmm... maybe I'll just turn off the option for a bit and put it back anyway.