Push is the new pull. And everyone's doing it. If you're still pulling, it's probably about time you stopped all of that, as Twitter opened up the site streams API to beta testers. App developers are salivating at the prospect of all those status updates being showered on them from Twitter's engorged hosepipe.
As a service, Twitter is experiencing increasing difficulties with the demand constantly being heaped upon it from the many client applications and mashups using the REST API. Switching over to streaming is definitely a more effective means of relieving all that pressure. The bonus is that apps built to use this torrent of data can benefit from real-time updates.
This is fantastic news for desktop Twitter clients and apps that do huge processing of individual tweets because it eventually means there could be no rate limit. Rather than polling and caching (to avoid the rate limit), all your app will need to do is listen out for updates, queue them and process when ready. Twitter's user stream API is also currently in beta, with desktop-only clients for now.
Access to the site streams beta will be opened wider than user streams, but is currently on a whitelist basis, requiring developers to request access and await authorization. There are some usage limits for now, although it's expected that these will be lifted as the API steadily comes out of beta. The Streaming API team over at Twitter HQ have also made it quite clear that functionality is likely to break during the beta and endpoints will definitely change during the shift over to a full-strength production setup.