So, MemberRemoved, seems to be firing pretty consistently, very nice.
It seems to be missing MemberAdded events now. It's not as big a deal, as getting out of sync doesn't seem to cause a client crash, and reloading the plugin will get the missing party members back, but definitely seem to be dropping MemberAdded events. (I think the members aren't showing up via :GetMember() either.)
Also, I only noticed this in a raid. In a fellowship, it didn't seem to occur.