We have been looking at Plesk as our next possible
control panel and I wondered if anyone is using Plesk
with remote DNS servers and a remote mail server?

According to Plesk this should be possible since most of the software is created in PHP.

It seems like almost all control panels, except the
expensive ones like Sphera, are hosting everything on
the same physical box.

If anyone has modified or added new functions to Plesk
I would really like to hear about it :) For instance; is it
possible to remove the annoying Plesk logo from the
users control panel? (I know Plesk's faq says it's
impossible.)

Thanks,

You should be able to use a separate dns and email servers.

The logo on top can be removed/replaced with your own in plesk's v1.3.1, if you are talking about the one at the bottom then you can only do this if you look around in the plesk's skeleton directory but i don't think plesk will allow it.