Caching data to reduce database hits

Are there any downsides to doing something like this assuming Foo data rarely changes?

class Foo < ActiveRecord::Base   class << self     def get_all_foo       @foo || Foo.find(:all)     end   end end

Is it ok to cache this data so you don't constantly reload it from the database. How long does @foo last? Just for the length of one request or until the server is restarted?

Thanks, Aaron