Updated - see below.
It appears that the micro-blogging service Twitter has removed the option to delete a 'tweet' once it's been published, making the service a haven for digital litter -- the trail of information about you or things you've said that perhaps you shouldn't leave lying around the web.
Publish a status update on Twitter slamming your boss - at 2am in the morning after a night out at the pub - only to regret doing so seconds after hitting the 'update' button, then you could be out of luck. As of yesterday (?) the trash can icon that used to reside next to Twitter updates has been removed.
A smart reader over at ReadWriteWeb suggests the likely explanation: Twitter has removed the delete function since it never really worked in the first place yet gave the impression that it did. That's because of the hundreds of services, including third-party clients and search engines, that exist built on top of Twitter's API. These services often cache Twitter's content or simply store it locally - such as the numerous Twitter apps for the iPhone - meaning deleting a 'tweet' from the main Twitter site doesn't necessarily ripple through to other Twitter services. If this is the true reason for deleting the delete option it would suggest that it could be gone forever. That's unless Twitter is able to design into its API a way to force all Twitter services to respect a deletion within a reasonable time period, although I doubt this will be possible.
Update: According to the official Twitter status blog, the delete feature will be back up later today. So it was probably removed temporarily to ease the load on Twitter's servers during election night. It doesn't, however, resolve the issue of third-party caching of Twitter posts, in which Twitter should at least warn users that a delete doesn't automatically take place across all Twitter clients or other services built on top of Twitter's API. (Hat-tip: Dave Zatz)