Access the bundled gems on your vagrant box from your host.
We all know that floating point arithmetic is imprecise but most of us pretend this isn't a problem until it reaches out and bites us.
In Rails you can easily use the link_to helper in your templates to create links that will generate HTTP POST, PUT and DELETE requests when clicked. You can do this using simply setting the :method option, but this ease of use hides a very real problem.
Out of the box Integrity expects that you will trigger all your builds using Github's post receive hooks, however you can trigger it with cron.
Take screenshots of your web pages with cucumber.
When setting up Mail.app on OS X to access your mail in your Gmail (or Google Apps) account via IMAP it is worth tweaking your 'Mailbox behaviours' and mailbox mappings to make them work together more smoothly.
Wouldn't it be nice to have a neat little an application on your desktop which allows you to search and view ruby docs.
The latest version of Screen (version 4.0.3 port revision 3) that comes with MacPorts is broken, but you can install an earlier one.