I think it's fairly obvious the slowness is not down to individual customers' computer or internet set-up. If this many are having problems (and those of us that bother to post are probably less than 1% of those experiencing the issue) then it looks like it's a Quickbooks software problem.  Dealing with each customer separately is NOT the answer. 

Mine is STILL running slow.  Has anyone else in this thread actually managed to get a resolution? If so, please share what you did as I'm losing faith in Quickbooks to do anything about this!