I come across this quite a bit and it manifests itself in different ways.
The situation I encounter the most is from people who don't seem to want to be interrupted, they need to finish getting their train of thought out at all costs before you butt in. Normally these people will fill gaps while they think with very long a loud varying versions of "Errrr", "Ermmmmmm", "Ahhh"... or repeat the next word they think they are going to say until their brain catches up.
I find it very hard to speak to these kinds of people in normal chit-chat situations, because they can sometimes talk for very long periods and cover a million and one things. I find my self having to memorise my replies as they waffle...
So, back to my question, is there a word this or this kind of person? Also although not really what this site is for, any tips on dealing with them :-)