It is near instantaneous for me and I am in Seattle,WA,USA. I've heard from many sources that AWS is slow if you are outside the US. Someone even brought this up in the AWS dev conference and the Amazon guys just dodged it and gave a generic 'things are being improved' response.

If http://www.instantwordsearch.com/ look up is painfully slow but http://www.instantwordsearch.com/backstage.html (statically served 103KB text) is very fast, then you can conclude that the problem is with my app. Otherwise it might be safe to blame EC2.

I am in Austin, TX and the front page took 5 seconds. I did not type anything or clicked anywhere.

The problem with EC2 and other super-managed hosting solutions (Joyent comes to mind) is inconsistency: I am sure they're moving VMs around, and occasionally they end up on overloaded servers.

But I am equally sure that EC2 does not oversell CPU/RAM resources and does not move VMs around. I don't think Xen even supports memory overcommit.

I bet most of that response delay is from the autosuggest lookup against the dictionary. It seems to be querying every time you enter a letter, so if you quickly type a word, you'll be initiating multiple GET requests, each of which hits the DB.