I think the McMansion idea is great.
I had a flashback of playing the board game Clue (http://www.hasbro.com/common/instruct/clue_%282002%29.pdf) with my siblings when I was younger. Specifically, I imagined a small team of developers in a large McMansion-Office trying to debug a large application saying things like, "I suggest the bug was commit'd in the kitchen, by Tom with his Custom Arch Laptop."
So for me from a founders perspective, the best kind of environment to get things started would be a company space that encourages setups like a cafe/lounge/coffeetable-style area for laptop users and those who need to be comfortable, focused, and relatively available with ease for discussion .. as well as areas of the workfloor where there are offices, for example, for those who need them, or hackylab environment for where its needed, etc.
Alas, this kind of mixed-format personal workspace organization is not so economical, and it usually requires someone be responsible for the estate, rather than just having a cubicle-cleaning service, etc. etc. All kinds of legal hoops, too, whatever.
But in my experience, this seems to be the case: the nicest 'kind' of workspace for a modern startup company in my opinion, is your average McMansion.
(If you can fit and find one local to everyone else who has to commute to it.)
I've seen great mixed-format startup scenarios in your average American mega-house, cubicle farm in the 4-car garage, massive lounge/rec-room space for the hackers, room #? of (4..6) bedrooms converted to shared office rooms, 2 or 3 to a room, for those who want 'a desktop' and a way to isolate themselves from the rest of the team, and so on.
Of course, this works if the house is clean and maintained as a work environment, and indeed if people don't live there but rather treat it as their place of work. That can be difficult to do in some neighborhoods.
Wouldn't it then be interesting to see some sort of 'office space plan' revolution occur in the broader sense, which accommodates all of these modes of operation, to implement a model you could name "Big Family Home"?
Instead of cubical farms, you find interior spaces analog to a modern home plan, s/beds/desktops/, centered around a common room/kitchen/meeting area, etc.
Generally the way I feel when I walk into a very large organization and its just endless row of cubicle, mind-numbing soviet khaki walls lit by brain-sucking illumination standards, all I want to do is go home.
That is a hard impulse to resist all day. If, instead, I'm in a place that accommodates a large number of peoples needs with some consistent attention to variety, usually its pretty hard to go home at the end of the day .. I really like going to a business where people are working and comfortable because they know where the kitchen is, and someone is making lunch for everyone while code gets written, clients are met, teams are having meetings out on the deck in the sunshine, etc. I'm sure there are movements towards this; but the cubicle-farm seems to have persisted for decades, alas, and for this I guess we must thank the bean-counters.