I like jetpack comments but i hate, that they only got option to post with wordpress.com user, facebook and twitter, but not using my own wordpress instalation users.
I know that when i'm connected it does not show jetpack comments. But i would have to add two forms - login and comment form, and in that case it has no added value and i could use just my form with fb and twitter connect.
I think there could be a solution using api etc. to make this callback somehow.