The MSN Search weblog has now announced that it is possible to use the system for tracking packages, or more specifically, packages from FedEx, DHL, UPS and USPS. Searchers can simply enter a tracking ID and some other tracking keywords and the Package Tracking Instant Answer will correctly construct the link. An example given is 'Where is UPS tracking number?' Additionally you could use the RSS feed for the search to really keep up to date on where your package has gone. Google has had this feature for years now, although it doesn't have an option for DHL.
Postscript from Danny: Yahoo added a package tracking command in 2004. It also doesn't cover DHL. Bloglines added tracking in March 2005, and parent Ask.com offers it as well, Ask's Gary Price tells us. He sends this example. Unfortunately, there's no help information that I can find on Ask that explains this further, not even in the Smart Answers section. Finally, check out PackageMapper.com, which we mentioned earlier this year. It provides the actual route your package is taking (though it wasn't loading when I tried today).