Daren - As one of the fastest runners on this thread, I presumed you must be pretty efficient already. Minamalist shoes normally have a drop of about 4mm to zero drop between heal and forefoot, flats a bit more. So as DD has said, your Achilles and calves get stretched further, so yes you ideally need to run as much in them as possible, for them to adjust. Compression socks help the problem, but don't solve it, you just need run more in them.
Red - MK again, you just want another wet,windy and freezing cold mara. One of the lasting images of Manchester mara that day was, a young lad getting one of his friends to take his socks off, so he could carry on with them on his hands, it was that cold.