Couldn't create database for ...

When you run rake db:create and get this error message

Couldn't create database for {"encoding"=>"utf8", "username"=>"root", "adapter"=>"mysql", "database"=>"project_development", "password"=>"topsecret"}, charset: utf8, collation: utf8_unicode_ci (if you set the charset manually, make sure you have a matching collation)

make sure the user you have specified (root/topsecret) in your database.yml has access to MySQL. You can check this by running mysql -uroot -p.