If you are looking to clean up a clogged up Twitter account, like the people asking questions here and here, this utility might be just what you are looking for (make sure you note the deletion caveats mentioned in those links though):
Announcing TweetDelete, the Twitter Mass Delete / Cleanup Utility that helps you mass-delete Outgoing Tweets, and Incoming and Outgoing DMs.
This is a very-much-beta version, and donationware. Use the feedback form if you find any problems (which I'm sure there are plenty), and if it proves valuable to you, feel free to donate to the cause.
Download TweetDelete here. No install required -- just download and run. : )
* * *
(Later Update: Having some issues with the update server; if you get in an endless loop of "checking for updates" clicking "Next" on the welcome tab, you can skip to the login section directly via the numbered tabs at the top. Should be squared away tomorrow if it's still a problem).
* * *
Update: New release (minor edits, modified expiration date) released today 07/20/2009. Apologies to the folks who got caught by the expiration period.
* * *
Update: 08/18/2009 Users have recently begun reporting "mo Messages found to to delete" as the result they are getting, and I now get the same result here. Looks like Twitter has changed their API, blocked this app in some way, or something along those lines.
Given the minimal support/contributions this app has received thus far, it's not high on my priority list, but I do plan to look into it eventually. Currently this app appears to no longer work, due to changes in the Twitter service.
* * *
Update: 09/21/2009 A number of daring souls have tried the app in its current form anyway, and feedback comments (built into the app) seem to indicate positive result. Your mileage may vary, but feel free to try it out, and let me know how it works for you.
Update: 02/10/2010 This current install is expired, and no longer works. An update version is in the works, however, and should be released sometime in the next few weeks.
* * *
Update 03/15/2010 TweetDelete has finally been updated, and now includes archiving capability. Download at the link listed above and let me know (via the built-in feedback form) how it works out for you.
* * *
Update 12/29/2010 Updated for newer Twitter authorization scheme, minor bug fixes, and easier save-to-text-file capability.
* * *
Update 07/08/2011 The current version is expired. Please check back in two weeks for the updated version.