As the title says, I flashed my N900 to the leaked PR1.2 using this blog post and then rebooted it.

Before I go into the details, I should qualify two factors that enabled me to do this:

1. I've reflashed handset firmware almost 1000 times on WinMo and Nokia devices over the years
2. I waited until enough other reports about leaked PR1.2 had accumulated so that my expectations of it would be reasonable

So if you've not got some experience re-flashing, I recommend patience and do your homework first!

The device rebooted no problem, and upon exploring the new firmware, here's a few things I've noticed/liked:

1. "About Product" screen indicates 'Version: 10.2010.12-9
2. "VOIP and IM Accounts" includes Facebook chat via the @chat.facebook.com server
3. "Sharing Accounts" includes an MMS service you can configure
4. "Photos" application includes bulk 'Share images' feature
5. "Contacts" application includes "Import from Exchange Server" feature for individual contacts
6. "App Manager" now includes an 'Update All' button when there are software updates
7. All original apps were restored, while some personal settings were retained (I restored from a backup to get missing apps/settings)
8. A new 'Email Widget' shows # of unread emails per account on the desktop (YAY!)
9. RootFS indicates 100megs of free space after restoring all my apps!

Things I need to re-implement/fix (because re-flashing eliminated them, just like any reflash would):

• Add 'reboot' option to power-key menu
• remove shadows from Desktop icons
• Restore system-wide use of Droid fonts
• Google Contacts sync via Nuevasync seems buggy (full functionality not yet working) [EDIT: Fixed by simply deselecting Calendar/Task in Settings panel, forcing Full Resynchronization of just Contacts info, then reselecting Calendar/Task syncing.]

I've also noticed that more of my original settings are retored with each reboot. So for example, upon first reboot my MSN/YAH!/AIM accounts were not shown in the "VOIP and IM accounts" panel, but after a few reboots they were.

Overall impressions are good. It works, it's not crashing, the browser is faster, and portrait-mode in the apps, especially Inbox and Conversations, is really great to have.

YMMV, and of course, your choice to reflash your device is all yours.

EDIT: I must add a BIG THANKS to Nokia devs for their work. Unleaked as this firmware may be, based on the improvements it brings to an already terrific device suggests (to me) the team is working hard on the right things. Thank you whomever you are.