The File Index is fairly useless, it exists merely for historic reasons. Besides keyword searches, some clients implement and allow searches by SHA-1 (urn:sha1). At the moment LimeWire does not support them and it is planned to re-implement this feature more efficiently using a distributed hashtable (DHT).

Almost all search results - except those from poor clients and some spam - carry an urn:sha1 along with them. This is the proper way to download the same file from multiple peers.