They are not all slackers living in their parents' basements; a recent survey by Pew finds that "13% of parents with grown children say one of their adult sons or daughters has moved back home in the past year. Social scientists call them "boomerangers" -- young adults who move in with parents after living away from home. This recession has produced a bumper crop."
Daniel Indiviglio at the Atlantic notes that a lot of people are living with less space- "a whopping 24% of respondents 18-24 years-old have moved in with a roommate as a response to the recession, while only 6% have moved back in with parents."
From an environmental point of view this might be considered a good thing, since more people sharing space usually means consuming fewer resources. But that is about the only good thing one can say about it;
Fully one-in-ten adults ages 18 to 34 (10%) say the poor economy has forced them to move back in with Mom and Dad.1 An additional 12% say they acquired a roommate. Hard times are leading young adults to put their lives on hold in other ways as well. For example, some 15% of adults younger than 35 say they have postponed getting married because of the recession; an additional 14% say they have delayed having a baby.
Everybody's footprint is getting a little bit smaller, whether they like it or not. More at Pew Research