Virtually all of the contract work my team does is remote since we service a global sales network and it is very doable. To be fair, I have met most, if not all of my “clients” face to face at conferences, tradeshows, and expos and the face to face part is helpful in building rapport.
I totally agree with chevisw that you need a good online meeting tool, we use GoTo a lot, but Join.me is easier and cheaper I think. And of course there’s always Skype too.
That said it also depends on the expectations of the work, if you’re generating concepts to meet a product plan that can be a simple arrangement and very doable remote. If you’re being brought in as a consultant on a large project or RFP with an extended timetable where team collaboration is key, then that can be tough. We had a large project with about a 3 year development cycle and while one of our product plan marketing consultants was local we set him up a desk in our office for 3 months. If you look at remote work on a per project basis in this way it could help you qualify what to take on and what to pass on.