CoBuying: Who's driving big market share; what are positive, potential negative impacts?

TWEET: Any insight into #CoBuying in #Boston? True 1 in 4 sales involves #CoBuyer, not family gifts money but real people (friends or #GoldenGirls) buying together, or some entity taking % ownership? Healthy trend, or sign of market’s overshot #affordability?

http://bit.ly/DiscussCoBuyerTwt

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Is this merely the fact that unmarried couples are buying together or is something else going on here?

Implications for affordability, and alternative housing like DIY micro-CoHousing communities, ie. a handful of people buying a unit or multi-family together as they've done at the peak of other previous market cycles?