Ours (in the UK) are hardly difficult:

• U - for everyone
• PG - 'Parental Consent' (parents should check first)
• 12A - recommended for over 12s, but younger kids may still watch
• 12 - only suitable for over 12s, younger kids won't be allowed in
• 15 - only suitable for over 15s
• 18 - only suitable for over 18s

I didn't think this film was going to get a PG certificate - the dementors and the scenes at the end of the book have always seemed scarier to me.

GoF and OotP will find it difficult to get PG certificates - the graveyard scene at the end of GoF and most of OotP are far too scary as they stand in the books for PG.

The 12A certificate was 'invented' for Spiderman, so perhaps it would be a good idea to use it here?

I think it was Steve Kloves who said that he didn't want to water down the books... if the books are scary, so will the films be!