I thought I had found Eupatorium perfoliatum (boneset)...but upon closer inspection I don't think so. Anybody know what this is?

It's a Eupatorium, but not Eupatorium perfoliatum. I'm pretty sure it is Late Boneset (Eupatorium serotinum).

http://plants.usda.gov/java/pr...

Thank you! Yup, I think you are right. This doesn't seem to have any good medicinal properties like E. perfoliatum, but it is pretty and attracts lots of bees and butterflies. Thanks again!