This is exciting, the load time is one of the things that is most painful for me when working with Rails. It's really great when you can just add gems and get things working quickly but the load time tends to shoot through the roof...
Spork etc help but you still end up spending a lot of time waiting.
Rails tests that takes too long are also painful too. If you try to speed them up, you might run into the problem of having to restart from scratch when you write stuff that need restarting to take effects.
Check out spork - https://github.com/sporkrb/spork. It keeps your rails code running so that you can run tests fast. Great for development, saved me 11 seconds every time I ran rspec.
Spork etc help but you still end up spending a lot of time waiting.