Felix Salmon crunches the numbers:
Twitter ... jealously guards access to its full stream of tweets (roughly 1,000 per second, these days). As of now, however, it’s signed a deal with Gnip whereby you can get a randomly-selected 50% of those tweets for $360,000 a year, which works out at $30,000 a month. You’re not allowed to republish them, but that’s OKthe people willing to spend that kind of money are likely to be high-frequency trading shops who want to keep the data as private as possible in any case.
2006-2011 archives for The Daily Dish, featuring Andrew Sullivan