Here are a few of the new features that will make it into the 3.0 release of the PSP firmware:
Remote Play - Remote play is a new feature in Firmware 3.00 that allows you to remotely control your PlayStation 3 from your PSP. This also includes the display of PS3 content on the PSP. "You can display a PLAYSTATION®3 system screen on a PSP™ system and play content that is on the PS3™ system. To use this feature, you must adjust the necessary settings on the PSP™ system and the PS3™ system." Using this new mode of playback, one can control the Photo, Music, Video, and Internet Browser features of the PlayStation 3 from a remote location via their Playstation Portable.
Video Compatibility - In this updated version of the Playstation Portable firmware, you are also able to play a few new video formats. The Motion JPEG format (M-JPEG), is an "informal name for multimedia formats where each video frame or interlaced field of a digital video sequence is separately compressed as a JPEG image" (Wikipedia). The PlayStation Portable plays both the Linear PCM and the μ-Law versions of the Motion JPEG video format. In addition, you will now be able to access the Camera (functionality) from the photo option menus, for quicker easier access when taking photos or video. Another nifty function is the ability to finally turn off Auto Play for inserted UMD Discs via UMD Auto Boot. (Thanks zerojay)
PlayStation Games - Here's the big tip you've been waiting for. Finally, Sony is going to drop their highly anticipated PlayStation One emulator onto the PSP. From the manual however, there seems to be a unavoidable catch. If you don't have a PS3, your not going to be enjoying PlayStation One games emulating on Sony's PlayStation One emulator for PSP anytime soon. From the manual it states that you must connect to the Playstation Online store with your PSP connected to the PlayStation 3 in order to download and play the games. In addition, they mention that you can in fact share the games, but you must activate the other system in the Friends menu as a PS3 Network Account.
More info can be found in the PSP 3.0 Firmware manual:
http://manuals.playstation.net/document/en/psp/current/