Learn how to add performance tests that automate benchmark and profile reports. Here I show how to find the bottlenecks to optimize a page. I also show how to compile Ruby with gcdata to get information about memory usage.
If your Rails app is content-heavy, consider organizing it in a tree menu structure. Here I show how to add top-level tabs, nested links in a side bar, and breadcrumbs to go up the hierarchy.
Instead of presenting a sign up form to the user, consider creating a temporary guest record so the user can try out the application without filling in their information up front. They can then become a permanent member afterwards.