Andrew Pollack will present a session about HASH at Entwicklercamp 2009 in Gelsenkirchen. Here is the session abstract:

This will be an entire session on using HASH values, HASH tables, and HASH maps.
We’ll use it to compile a report in memory from two different data sources without reading and sorting all the documents.
We’ll use it to compare a million rows of data from an SQL call against a database of Notes documents to look for field updates without ever reading any of the notes documents.
We’ll compare two databases with a million records each, and pick up the one that changed between the two in seconds — reading only a two column view that isn’t even sorted.

Sounds like this will be great fun 🙂