Latency is the usual for international [600-800 ms]
Error Rate? Now i obviously don't play it 24-7,maybe an hour or two per session and
during that time i usually don' get alot of "errors". Main "errors" are either insane lag [the source is tricky to determine as it's a combination of Anet Servers,3G and the fact that they stream content "while you play" [ i.e. patches/enhancements are delivered this way] ] or of course a plain disconnect [which thankfully don't happen that often].
I'm in Stellenbosch
The game show the speed at which data is streamed in-game and i've had speeds of up to 24 kbytes/sec but just as often had it at 1 kbytes/sec as well [speed seem to vary quite alot though]. I'd say you're fine with about 10 kbytes/sec and the usual latency, anything slower and you start feeling the lag.
Have to keep in mind GuildWars is heavily based on "instanced" areas. This means every team gets their own version of the map/zone, which makes for less lag in cases as there is only your team to keep track off in a specific area. Same happens with Arena-battles, Two teams goes up against each other, they get their own map [so it's not just an open landscape where everyone run around like everquest/ultima]. There are of course "hubs" or "outposts" where you can do trading/create teams/show off and such but that's that.
This does not apply to GuildWars only, i also trial-played Eve-Online, DAOC, Anarchy Online and WoW with the same kind of performance on 3G. So as long as you stick to MMORPGS you should be fine imho [anything else like counterstrike/UT/BF2/COD is probably not going to work well, nevermind the bandwidth those games use]