There are some bugs and problems being reported with PR1.3. You might want to wait a few weeks and see what people have confirmed before deciding for sure.

One which particularly bothers me is "Calendar Alarms Stopped Working", http://talk.maemo.org/showthread.php?t=64594
It might be a one-off for the unlucky person though. Let's see what others report.

(If there are any typos or missing punctuation in this message, it's the N900 losing keystrokes as it does in web forms... )