We created this service because we use Craigslist to look for some oddball items that aren't always available (lately Ted has been looking for a lot of baby-related stuff). We got tired of having to constantly check Craigslist to see if anyone had posted one of the things we were looking for. We thought it would be nice if someone sent you an email when the item you are looking for is posted.
Here's a brief tutorial:
Here's a search example. I'm looking for tires and wheels in the 245 and 235 size range. I entering into the search criteria box:
wheels | wheel | 245 | 235
Which tells it to look for the keywords "wheels" or "wheel" or "245" or "235". Pretty cool.