Why not? A bubble occurs when people over invest due to mass hysteria. Whether the investments occur through a public exchange, or through second markets the psychology is still the same.

Facebook may have a valuation of $60bn, but actually the ammount of cash invested is only $2.34bn [http://www.crunchbase.com/company/facebook] so that would be what was lost if it collapsed. Same for Twitter, actual investments are $360m not the $7bn it maybe valued at. Though I guess it's unknown how much has been traded through secondary markets.

My point was, what effect would it have on the NASDAQ or any stock market? And would it mean that anyone investing in bonds really lost anything?