I can't see Twitter surviving if their long term strategy is to sell firehouse access to their competitors. Relying on your competitors to keep in business is a bad business plan to say the least.

The way I see it they're pretty much screwed. They're going to have to start looking at different ways to monetize and they don't have many choices. Injecting adds into everyone's Twitter stream will mean a drop in users for sure plus it will contaminate the firehose. Relying on smaller developers to pay for API access probably isn't going to generate enough revenue especially if other options are available from Google et al. Once again, Google will destroy yet another marker with free...

Of course one also has to wonder if Twitter isn't just a "pet rock" that will run out steam on it's own.