You mentioned me, but I'll post anyway.
I would say I'm a casual user of Linux. I know enough to be able to help some people install it, and I use it regularly, but I don't really contribute to it as I don't know C/C++.
I just decided one day that I would install Linux because I was annoyed at Vista taking control away from me and for programs with basic functions (like converting media formats) being £20 closed-source applications on Windows but free and three clicks away from installation on free OSs [since then a lot of those applications have had Windows ports].
I wish it was acceptable in the wider world to use Linux of one's own choice. So if every common software package supported Linux and every peripheral at least let the community maintain an open driver for it. Part of that is it becoming more popular, but it won't be until those changes are made. I don't see it breaking that cycle unless major OEMs make Linux an option on most new PCs (not just special Linux models that are overpriced and hidden away on the website) and then promoting it as cheaper than Windows or requiring fewer resources or getting a lot less malware, all of which could persuade people if they knew.
Linux is suitable for 90% (EDIT: a significant proportion) of computer users (the internet, e-mail and MS Word type), but the only users who are aware enough to know about it are those tied to Windows by their work (Needing Adobe or Microsoft tools) or video games.