I use vnc

firefox on my dev box

safari on my living room mac mini G4 (vnc from dev box)

IE? i call my friend to test or just go to internet cafe

iirc vnc server can take external ip ... so presummably you can connect to vnc server half globe away and see how people there connect to your site

of course the bandwith is shared between browsing and vnc-ing so u will get less than accurate experience