Is anybody in a situation which you have an external supervisor? maybe such a researcher is professor at a different university and you stay far from him, doing research and sending him/her your progress through email. Does it work? Should it be avoided by all means? Might it works? Does it depends on wether you have a second supervisor? Is it worth? Is it dangerous? We all know researchers move frequently from one university to another, so I guess many people are currently in such circumstances

it is common to have an external supervisor. I don't think they could be the director of studies though, they can be first or second supervisor depending on your university's rules. At some universities, the director of studies is also the first supervisor, in that case the external can't be your first. There are some politics involved, so you cannot just bring someone in, you have to follow procedure.

We talked about supervisors on this thread a bit the other day: http://www.findaphd.com/students/showmessage.asp?thread=6320&cat=4&threadpage=1&newview=1

and i forgot to say, it works. You can always visit them at their institute once every two months or something like that, and keep in touch via emails.

One of our full-time students lives in Europe. He comes over several times a year but conducts most of his meetings via flashmeeting. I know it's not quite the same as having your main supervisor as an external as he is registered at this uni, but I thought the method of meeting was interesting. He says it really helps him as he is a non-native English speaker. He doesn't take notes, but listens to the Flashmeeting recordings afterwards and this provides a good record.