I installed 6.1 without any problems.
I didn't need to perform 2 installs - after first both PDA and Phone were showing new versions.
I restored my data and reinstalled applications - no problem.
E-mail (Outlook), wireless works fine as before - no problem.
Previous applications work fine.
I like the new task manager and the automatic new email signature (Send from Mobile...) - nice touch.

But I still have my biggest problem not fixed - BLUETOOTH :
(See my post: http://pdaphonehome.com/forums/742853-post45.html.)

The problem still exists - not fixed!
Prius disconnects the pairing shortly after initial connection. The only way to restore it is to power off and restart a car!

And because California requires now hand free cell phone usage while driving, I'm seriously considering other options (phones, PDAs).
I really hoped that 6.1 would fix this problem.
It's not Prius - my previous Motorola and PPC6600 didn't have an issue.
My wife's LG does not have a problem.