Validating Flashback Database

Oracle  10.2.0.3 EE on RHEL 4

I am considering using the following method for application upgrades
in the future:

(N.B. Flashback Logging is Disabled)
1. Shutdown DB
2. Create Guaranteed Restore Point
3. Upgrade application
4. Test application
5. Drop Restore point

I am proposing to use the above method instead of doing a cold backup
before the application upgrade.  This will significantly reduce the
downtime required for maintenance and will allow us to restore the
database to a point in time very quickly.

My concerns are:

1.  Flashback database is very 'black box'.  How can I be 100% sure
that it has flashed back every block consistently.  With a cold backup
I am 100% sure that I can copy the files back to the original location
and everything is exactly as it was before the change.  If I use
flashback database I am effectively relying on a relatively new
feature that could potentially have bugs.  For example, flashback
database failed to reverese a tem****ary tablespace resize operation on
one of our development databases.

2.  Does flashback also reverse changes to all data dictionary
blocks.  i.e. can you reverse (or flashback) an Oracle patch..?