As an amusing side note: a friend of mine worked for a large local ISP that shall remain nameless. They used the following as production code:

cd /some/path/name
find . -mtime +30 -print | xargs rm
[download]

The problem, of course, is that this was run as root from the root directory. My friend got paged out of a movie when /some/path/name turned out to be invalid. You can imagine what happened :)

The other problem (and I haven't tested this, to be honest) is that the above code will not get rid of filenames with spaces. Of course, that's pretty obscure, so I doubt it would come up.