You can use Airbrake for free (https://airbrakeapp.com/account/new/Free), and it takes about 3 minutes to setup and you don't have to think about it. Sure, you don't get automatic deploy notifications built into Capistrano, but I've certainly upgraded my Airbrake plan for various apps in the past and will do it again.

Why would I want to concern myself with maintaining another app when I can just use Airbrake?