Moving from .Net/Java to Rails

Some pointers:

If you need a memory cache, have a look at http://www.danga.com/memcached/
Have a look at http://dev.robotcoop.com/Libraries/ for plugins and libs.

Rails also has great caching features built-in:
http://api.rubyonrails.org/classes/ActionController/Caching.html

Rails includes support for the script.aculo.us autocompleter-- basically, it's two lines of code and you're there. Of course you can customize, too.
Demos and example code:
http://demo.script.aculo.us/ajax/autocompleter
http://demo.script.aculo.us/ajax/autocompleter_customized

Best,
Thomas