I am seriously beside myself with vendors who don't respond to at least say "Hi! Received your email, we're swamped now but will get back to you with X days!"
I can't tell you the number of emails that have gone completely unresponded to by my caterer and stationer. When they do finally get back in touch with me, they're sweet as pie, apologies all around, and do great work. But this lack of communication just two weeks before the wedding is grating on my nerves.
My florist and DoC at least have always been responsive, kind, helpful, and everything a vendor should be!