For inspiration, please read the 50,000 foot piece.
Here's what I did today in EC2-for-Poets land.
1. I wanted to get an idea of how many servers were running, so I pushed an update that has each server ping one of my servers once a minute. I keep a table there indexed by IP address with the number of times it pinged and when it last pinged.
2. I am now running a micro-instance, based on a discussion in the comments under the Howto. I'm going to leave it running a while and see how it performs. Micro-instances are much cheaper than "small" ones.