Louis Rosenfeld has what looks like a great set of information architecture heuristics for search systems)

Searching, he says, consists for most people of the following:

1. Locating search: Where is it?
2. Scoping search: What will be searched?
3. Query entry: How can I search it?
4. Retrieval results: What did I find?
5. Query refinement: How can I search some more?
6. Interaction with other IA components:
7. Finishing search: What can I do now that I've done searching?