I like "faces" or if you're a fan of Jim Carey it could be "masks". For me "faces" denotes what we present, and "Masks" denotes (for me) what we hide, so I prefer the "faces".

I was thinking of giving contributors the choice of icons (similar to the icons of the thumbs up/thumbs down for like/dislike) to indicate if the role is personal (face with baseball cap or hair down) or more formal (face with hair up, clean-shaven with glasses and/or tie)

I was just thinking of adding contextual themes (skins) so that contributors can add posts to their more formal space or less formal.

Ah ha! Interesting. In theory, the access control rights should already be usable to specify an audience as you suggest. Technically that can be done already using collections (you could create a collection of people you are following that are friends, say - in effect you are tagging them by putting them in a collection) but they are not simple to use: something like the icons you suggest might help with that problem - it would at least make it easier to identify the people you are looking for when, like me, you have a really long list of groups and collections to choose from. 

The context switcher is meant to allow people to create an indefinite number of spaces (well - screen limitations and usability probably limit that to a handful or two in real life) that can be formal, informal or whatever you wish, but they are not going to be places that you post things into as such, though you could set them up to mostly work that way if you like. The way it works is that each space (context/facet/face/avatar/etc) can contain the same varieties of widgets you currently only have on your profile and dashboard, configured and arranged differently in each space to show different things to different people in different ways: much as you can now on those pages, except that instead of being limited to doing it on your private dashboard and public profile you will be able to create further widget-filled pages (technically, as tabs of your profile) and we will give you increasing control over appearance, content and layout. You could therefore create a tab that only showed things in widgets that are accessible to friends, if you wished, and another for everyone else. And another for your course tutors to show off your work. It's very flexible! We'll also be doing the same for groups.