Similar to Slideshare, Slideboom allows you to publish your presentations to the world. They do seem focused on the PowerPoint world but you can also upload a flash version of your presentation. What I really like is the PowerPoint add-in by iSpring which integrates with SlideBoom and allows you to publish direct from PowerPoint while converting to Flash. They also do a really good job of taking a presentation that has animation, sounds, music and is entirely automated and keeping all features intact, converting to flash and allowing for upload to the site. Slideshare I found was not able to handle animations, sounds or music ... so depending on your purpose and intent of the presentation Slideboom is much better in that regard - although as of now it is not as popular. It will be fun to see slideboom, slideshare, authorstream and others go at it.