Using the technique described in this post:
http://paulmayne.org/blog/2007/11/how-to-remove-broken-or-dead-tracks-from-itunes/
I was able to get a list of all of my broken links in iTunes. The vast majority of these files have just been moved to other directories on my hard drive.
Are there any apps available which will just check my hard drive for the missing files, and then update the links if and when they are found?