If your using Dalli and Memcached, ensure you are running the latest version of Memcached (at least 1.4 or greater) otherwise when starting Rails, the server will hang. You can upgrade Memcached easily enough with MacPorts (if that's what you're using):
sudo port upgrade memcached
If you haven't installed memached using MacPorts before and just have the version shipped on OSX, then do an install:
sudo port install memcached
Reference: http://www.mikeperham.com/2010/08/30/dalli-memcached-for-ruby/
