Just flashed mine with the global firmware. Contacts and files were left intact, restored settings from backup.

First impressions:
1. This is obviously old news, but it's nice to actually be able to dial USSD codes directly with the Phone application.
2. Maps seems to get a GPS lock faster.
3. Email client loads mail folders (esp. my gigantic Gmail inbox) faster
4. Long press for numbers and symbols is also very useful
5. Qt 4.6 included by default. I'm a developer so this is useful for me.
6. Email widget is nice but I want it to be able to show read messages as well. I don't like having to see the (no unread messages) message.
7. I still can't create playlists in the media player. What's up with that?