Examples:
  -craigslist.com
  -ebay.com

Example - checking an ebay.com search using Quickthreads.

Searching for something on ebay.com or another auction site? Most of them provide an RSS link you can use after doing a search. If you copy / paste this link into your Quickthreads account, you can monitor new items as they are posted, or check on existing auctions. Here's a screenshot from a recent ebay search, with the RSS button circled. Usually the RSS link is at the bottom of the page somewhere.