I use the service NewRelic for monitoring rails applications. In the newrelic.yml file, there's the following option (that's commented out by default):
# Enable textmate links
# textmate: true
How do I enable this and what capabilities does it give me?
That'll give you links in the stack traces that appear in Developer Mode (http://localhost:3000/newrelic). Those links will open the relevant source file in TextMate.