I use Exchange 2000 Server's full-text indexing feature (MSSearch). I recently tried to stop an indexing session, but I couldn't because Exchange System Manager (ESM) got stuck, and the indexing process didn't stop until I killed it manually. What happened?

The indexing service runs synchronously, which means that after ESM issues a stop request to the service, ESM must wait until the service responds. The indexer doesn't necessarily stop when you tell it to, which is what makes this problem visible. When you stop the index crawl (by finding the store being indexed, right-clicking it, and choosing Stop Population), you must wait for the service to stop on its own. Killing the service manually might work, but it might also corrupt the index, requiring you to rebuild it. Microsoft knows that this feature is, shall we say, undesirable, and I expect that the company will fix it in a future release.