Upgrading to a new version is always risky, especially if there are a lot of changes between the two versions (since the latest alpha release more than 400 commits were made). So it is no surprise if some stuff breaks.
In the pre-beta two files have been removed which may affect your application, even though it is rather unlikely someone used those files: dbo_pear.php (i.e. support for PEAR-DB) and neat_string.php.
Something else that caused trouble for me, is that the following code snippet returns always true in a controller action:
I don’t know whether it is a bug or a feature that this variable is always set, up to now it was only set if you submitted a form as far as I know.
Anyway, it seems like the upgrade caused less trouble than expected ;-)