What bugs me the absolute most is seeing that my message has been read and I don't get a response.
I'm probably different than many in that I usually one have one or two providers in mind when I'm looking for an appointment. I won't send out 10 pms hoping to hear from somebody. I want to see who I want to see!
I do think if you advertise on this site and unless specifically stated in your ad to contact you in a certain manner that you should be responding to PMs