I learned the fun way (i.e. wasting an hour) figuring out that rake db:seed fails if db/seeds.rb doesn't exist. So if you're using seed_fu, you need to make sure you don't delete the original db/seeds.rb.
I also wanted to be able to have seed_fu run from a rake db:reset which wasn't happening by default. However, this can be enabled simply by adding
to your db/seeds.rb. This causes rake db:seed to call through to seed_fu, allowing everything to play nice.
+1 On this, I didn't realise this either.