IMO, Twitter is the poster child for the tech bubble. They have users, which is their only claim to viability, but notably, they have never made a profit. Currently valued at around $10 billion with 350 million active users, that's about $29 per user. You'd be hard-pressed to find an investor so foolish that they would invest $29 in each of their users and hope to make it back if it were stated in those terms, but people have rushed to invest in a company which only has users, and whose attempts to monetize users through advertising have correlated strongly with loss of users. There can be little argument that Twitter's price has become entirely detached from its value.

That doesn't of course, mean you couldn't make money by investing in Twitter. You can make money by investing in overvalued companies as long as you don't hold onto your share until it busts. One profitable route would be if Twitter does get bought by a larger company. The market as a whole will lose on Twitter, but local maxima can be more profitable than the whole.

But at a personal level, don't be naive about this. A lot of people are investing, not just money, but time and energy, in Twitter or startups like Twitter. If you find yourself thinking that Twitter is a company with any real value, you should take a step back and evaluate whether you're being wise, or whether you've fallen prey to the unbridled optimism of the tech bubble. Twitter's position as poster child for the tech bubble makes it a good litmus test for people's understanding of the industry, and I suspect it will correlate very strongly with who loses everything when the tech bubble collapses.