Some of the fixes include Battery enhancement on the Lumia 800, audio improvements, "call end" bug fixes amongst others
Here's the email from Yvonne at Nokia Care about the new update
Good news! We have brought forward the software update schedule for our Nokia Lumia 800, and have begun rolling out the latest update 1600.2487.8107.12070 to India and Singapore. This update will gradually be available for more markets in the coming weeks and we will keep you informed via our support pages as well as via a similar announcement here on Nokia Discussions Forum, once we add additional markets to the roll out.
As this is not a mandatory software update, not every country or network carrier will make it available to their customers. However, all features and enhancements will be included in subsequent software updates. If you have questions if 1600.2487.8107.12070 will be available for you, please check with your local network carrier.
The new Lumia 800 update brings the following enhancements:
• Enhanced battery standby and talk time performance
• Battery capacity icon instead of question mark on top right of screen
• Improved bass in audio performance
• Soft-key illumination at all brightness levels
• Fixes for device performance issues including self-reboots, freezes and call-ending
As soon as the update is available for you, your phone will display a notification on your Homescreen or you can check for available updates manually by going to Settings > phone update. To update your phone, please follow those 4 steps:
1. Install the Zune software (Windows) or Windows Phone 7 Connector (Mac OS) on your computer. You'll need this software to download the phone update.
2. Connect your phone to your computer, using the USB cable that came with your phone.
3. If the Zune software or Windows Phone 7 Connector for Mac doesn't start automatically when you connect your phone, start it manually.
4. In the Zune software, click Update Now (in Windows Phone 7 Connector for Mac, click Install Updates). Make sure you keep your phone connected to your computer until you see a notification that the update is complete.
Yvonne from Nokia Care
It's not clear how the update will be rolled out, only that India and Singapore will be the first to get them.
So hold on to your seats, you can hold your breathe if oyu want (though I highly advice against that), Nokia has proven it can distribute updates to everyone in a timely manner!