Lesson N: Use a system that doesn't require you to manually remove cache files. Seriously.
1) Cache the page in memcached, which would give me access to an easy time-based expiry syntax.
2) Page cache. Instead of cleaning the cache with a one-line cron script, write a 10 line cache sweeper. Then, install a plugin to periodically execute the sweeper... or execute it with a cron script.
3) Page cache. Delete with a cronjob.
Why I didn't do #1: Memcached is overkill for my needs, and keeping another process running on the VPS just gobbles its 256MB of RAM even faster, while giving me another potential security/uptime headache.
Why I didn't do #2: Doesn't eliminate the dependency on cron, it just moves the actual delete operation from a single line in the crontab to more complicated Sweeper logic in the app. That is logic I'd then have to actually maintain and whatnot. (And doing #2 wouldn't have helped me if I had executed the Sweeper job as the same user I executed rm -rf as, because it would similarly have been unable to remove the file.)
I might be careless but I don't make choices totally at random. ;)
Why not upgrade? On Slicehost, going from 256 to 512 MB is only $20 extra. If you're running a business on it, I think that's a pretty reasonable expense, especially if it can save you even a little time (within reason).
http://api.rubyonrails.org/classes/ActionController/Caching/...
Removing them with a cron task is usually the worst way to solve this problem. Using the expire_page method is the correct solution when the updates are being done as a result of a user's action (updating/deleting/creating a record). The problem here was that they weren't being done by a user, but automatically by the system.