To give you an idea of how it is at the moment.. in teh Atomicblue demo I have little if not no net lag (the odd player teleporting a short distance thats about it) and I live on the opposite side of teh world to teh server ^^ as well as a completely differant hemisphere... and... I only have a 56k modem.
So you dont realy have to worry about it ^^... the information you get is basicly just 3d co-ord\'s of the people and creatures around you, weather there running or not, action being performed to update animation etc, and you only realy get stats and the like on a need to know basis.. ie if your fighting the thing in question.. so not alot of information is passed around probably 1-2k a second, and most modems handle that as easy as pie. HOwever Im baseing that on what I assume and have seen in other MMorpgs, im not sure how the coders are coding it for PS.