So there's a few things not stated in the official update notes. All this info from GAF:

Official update notes:

Support for PlayStation Plus has been added.

[Email] has been added to the home screen.

You can now transfer content between the PS Vita system and a PC using Wi-FI.

You can now transfer a folder from a PS3 system or a PC to the PS Vita system.

[Maps] can now display weather information.

The display performance in [Browser] has been significantly improved.

The buttons on the PS Vita system can now be used with more applications.

In [Settings], you can now set how you will be alerted depending on the notification type.

Turkish has been added as a system language.

In addition, the usability of many features has been improved.
You can squash and stretch the PSone screen to your liking now. So custom aspect ratios.
PlayStation Mobile 1.00 Runtime Package now available

near ui has been changed, much better
Friends app's LiveArea now shows your friends' activities. That was a nice addition.
I think screenshot function is instant now. No more 'please wait' window after you screenshot

You can now send messages with friend requests!
Few changes I've noticed that I don't think have been mentioned

- Playback menu is much bigger, and centered
- You can now go in super slow mo. (1 frame a second?)

- You can now download updates to games without needing to insert the game card first.
- PSM version installed listed under settings
- Under trophies, the buttons for PSVita System/Playstation Network look different. (Smaller?) They also don't make a noise when you press them.

And it's kind of unrelated, but there's an update to the Skype app.
Browser changes:
old score

new score

Also, it is now 100/100 on acid3 test. Was 99/100 before

Some awesome changes. The Vita OS is actually very good and they've continued to better it. I'm impressed