Here's something I just learned the hard way.
If you edit a crontab with "crontab -e", cron won't reload the updated crontab immediately. Changes will be read at 1 second past the next minute boundary. For example, if you change the crontab at 10:54:32, cron will reload it at 10:55:01. This means if you're trying to test how something runs under cron and you're impatient so you set that thing to run at the next minute, you won't see it run!
I spent a good half hour chasing my tail on this one. Set the test entry to run 2 minutes ahead instead.