No dispute with you there - I mentioned some possible metrics, but those you mentioned are also clearly important.

I was commenting on the question about usability testing (which yes, should include testing of experienced users); I don't have the information to make a judgment on the Edit button; I presume Google and Github both saw something in their testing that led them to make their design decisions. However, I am interested to know, in Google's case, what improvement, and what problems, they saw from this particular change. Anyone work on the new Google Contacts?