My workplace is practically near the servers (read: same city) but for collegues working abroad, in other continents the connection speed for their network is much less, and even when they connect to a server that is outside their network performance goes down rapidly.
It would help (and create a bit of awareness) to have the option to specify your connection speed, so you can test your application for different kind of users. Preferably somewhere from the statusbar in Designer. (I believe WYSIWYG editors like Dreamweaver have it) .
I know this will not tackle all or mimic most of the problems users face, but at least I can see how my app works at different speeds. In that way I can search for and test performance improvements.