no amount of googling or reading of man pages has been able to answer this question for me. Perhaps there's someone knowledgeable and kind enough to be able to tell me....

Is there a daemon that will do the job of updatedb continuously, updating the database as and when files are created and modified? I find locate very useful, but don't like listening to my hard disk suffer each day as updatedb runs as a cron job.

Another thing to satisfy my curiosity: does running updatedb cause much wear on the disk, and cause problems in the long term?

This is not possible, because the program doesn't know what files have "changed", it just updates the DB for every file.

You'd need some sort of file system extension, which may be possible in ReiserFS4.