I guess for many people the idea of an egregore and it's uses can be difficult to relate to. Even Janet Farrar & Gavin Bone, in their book, Progressive Witchcraft decided to opt for the term Gestalt Mind, which I find interesting. I asked several psychology friends of mind (some qualified and some still studying to see if anything was fresher in their heads) on what the "Gestalt Mind" was precisely and while many were able to ask me did I mean Gestalt Psychology no one knew what the Gestalt Mind was or how precisely it operated. Having researched this online a little further I found references to Gestalt Psychology alright and at first wasn't impressed as the Wikipedia page needed HUGE citation help.
Anyway, looking online I found that Gestalt Psychology holds with the idea that: "The Gestalt effect refers to the form-forming capability of our senses, particularly with respect to the visual recognition of figures and whole forms instead of just a collection of simple lines and curves. In psychology, gestaltism is often opposed to structuralism and Wundt. The phrase "The whole is greater than the sum of the parts" is often used when explaining Gestalt theory." (- http://en.wikipedia.org/wiki/Gestalt_psychology). Looking at it from a sociological perspective I find myself surprisingly nodding to the idea that to some extent this could hold mustered. When groups of people get together with no definition of who's in charge rules will still formulate as a consensus is reached and people follow their own prescribed hierarchy possibly perceiving a "whole image" rather than the constituent parts. Basically Gestalt Psychology believes that the whole is perceived first and then the symbolic breakdown begins. Which Structuralism holds that the parts came together to form the whole and the parts usually come from symbols and therefore fall under the remit of linguistics.
It should be explained that Progressive Witchcraft does NOTHING to extrapolate on what the "Gestalt Mind" is at all. Perhaps the authors simply feel that the mere mention of the word such suffice (even if the school of thought is so obscure).
Generally speaking an egregore will be cultivated in a magical context via the more traditional paradigm of the group creating a thought-form from constituent parts all relating to specific symbolism. Anyone that has worked with Telesmatic workings will be aware of the process. First the form is visualized and then the ensouling/charging is done usually through ritual chant or dancing. Sometimes the image in magic is built on a talisman as a "key" to activate it for future use. Another method is to create an Inner Temple space on the astral realm with the assumption the astral realm holds all past, present and future symbols for the group to utilize. So in a group setting the symbolism would be the language of the tradition, for some this may be Arthurian legends or Egyptian myths and so on.
One thought-form experience I had the year before last involved a visit to a passage grave called Four Knocks. I decided to "test out" the guide's assertions that there was a guardian there (he was quite sensationalist as he's there to make mullah of the Yanks!
lol) by leaving an offering of a crystal to the carving at the entrance when a form stepped forward and thanked me. I'm relatively confident that the entity was created through the shared expectations of annual visitors to the place because "he" didn't feel old to me. A nature spirit feels free and wouldn't generally be programmed. The ensouling or charging aspect to thought-form creation usually entails a programming part of the ritual to give it instruction. I have other stories for comparison.