The latest auction of Twitter shares on Sharespost valued the company at $7.7 billion, which is almost twice as high as Twitter’s valuation after a round of funding in January.

According to Sharespost, a secondary market that lets investors trade with otherwise illiquid assets, investors have agreed to buy 35,000 shares of Twitter’s Series B preferred stock at $34.50 per share. Multiplying that figure with the 223.7 million fully diluted Twitter shares listed by Sharespost one gets a staggering $7.718 billion.

Facebook has experienced a similar growth on secondary markets in the past two years: after being valued at a mere $9.5 billion in November 2009, a round of funding in January this year valued it at $50 billion, with the latest trades with the company’s shares pushing the number even higher, to $65 billion.

What do you think? Are these valuations based in real expectations of these companies’ future performance, or have we entered another bubble? Please, share your opinions in the comments.