I have one rubyonrails app that turned really slow in development mode. Everything is fine in production, but even a simple "hello world" takes seconds in dev. I checked the session store and every possible reason i found on the net, but I didn't find the problem. Am I missing something that is common knowledge? "Completed in 1657ms (View: 226, DB: 39)"
Development is definitely slower, because it reloads all components. Production mode only loads the components when the server is started.
If you find your app is still too slow in Production mode then you can start hunting down bottlenecks. You can start by optimizing DB queries, with :include and indicies. You can also try removing your gems and plugins systematically to find the parts that are slowing down your code.
Create a new app, see if that's slow too - that'll point to your server stack (apache, mongrel, passenger, etc.) rather than your application. If it's just your application then google rails profiling - and pick one of the many options for profiling an application.
This is usually the case if you are running webrick, its so slow it makes eyes bleed.
Try installing mongrel in dev
gem install mongrel