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 temporary 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..?