The first group are novice users. These are people who use a computer, but the concept of an operating system or the idea that windows isn't just "part of the system" and not removable is alien.
I would suggest there is an "intermediate users group. This group is not afraid to play around with different OS's, hardware and software and know how to configure their software of choice. However they rely heavily on configuration tools to apply much of the digital glue to make their systems usable and/or secure.
The second group is "advanced" users. I think most of us would fall into this group. We understand OS's, hardware, software and all the digital glue that holds it together.
The third group is educational users. These would be people who work in some education institution and they're interest in linux would be from the standpoint of deploying it for cost savings and/or using it as an education tool for teaching.
The forth group would be corporate suit types. These are the people who read the trade rags, but don't have a clear understanding of what linux. They've read lots of conflicting FUD on the subject and aren't sure how linux could be used in they're environment or what the real TCO would be.
--mike