You can learn more-or-less all there is to know about the new text chat feature from the short video below; it's not an overly complicated system, and there aren't that many ways to use it. Basically, you can chat, either one-on-one or in a group of up to 15, through the same single window. The chats run in the background, which is to say they can be used in-game, so PS3 owners can finally perform what have become the three holy sacraments of multiplayer gaming: strategizing, taunting one another and hurling nonsensical racial slurs in no specific direction. It's no voice chat, but could be workable with a keypad attachment or wired keyboard.
It's generous to call the new video portability an additional feature; more accurately, we've seen a pointless prohibition lifted. Now your PS Store videos, whether purchased for the PSP or PS3, can be stored on an external HDD for later viewing, which is especially useful if you've got the wimpy 20GB model. The update should be available now—let us know how it works in the comments. [PS3 Blog—Thanks, Joel!]