I very strongly doubt that they will be unable to profit. They've just managed to rack up so much funding without doing so that they haven't made it a short time priority yet. If they had no master plan for huge profitability only idiot VCs would continue investing.

If anyone has an idea for how they will make money, they are keeping them to themselves. I haven't heard of a single plausible idea.

Twitter will make money using premium accounts, selling access to the stream, selling their own premium clients, and selling targeted advertising.

You know they have considerable income right now, right?

Still, VCs can waste a lot of money on a bad idea with no real plans of revenue generation. Boo.com & Napster were both great examples who burned around $120m each (Boo's revenue strategy was apparently to spend $120m wooing big names in the fashion industry and throwing parties, whereas Napster's strategy was to spend $120m getting sued for enabling music theft).