Comments on: webOS 1.4 Now Available
The full changelog is now posted on Palm's support page. Major new features include: video capture and clip editing, performance and battery life changes, various new messaging, contacts & calendar changes and options and updates, LED based notifications, new ringtone/alert options, mail improvements and various other system tweaks and such.
webOS 1.4 also brings support for the Adobe Flash 10.1 Beta plugin. Adobe will presumably release their Flash beta for the Palm Pre sometime soon via the Palm App Catalog.
Update: Verizon users are reporting that the update is now available for the Pre & Pixi Pluses.