Why I've got no crontab entry on OS X when using vim?

Just follow these steps:

1. In Terminal: crontab -e.
2. Press i to go into vim's insert mode.

3. Type your cron job, for example:

   30 * * * * /usr/bin/curl --silent --compressed http://example.com/crawlink.php
   

4. Press Esc to exit vim's insert mode.

5. Type ZZ to exit vim (must be capital letters).
6. You should see the following message: crontab: installing new crontab. You can verify the crontab file by using crontab -l.

Note however that this might not work depending on the content of your ~/.vimrc file.