Most applications write useful debugging information to logs. On Heroku, these go to standard output by default and are eventually discarded.
We typically use Logentries to accept logs from Heroku and other sources. Once sent to Logentries, you can search previous logs and set up alerts for errors outside the Rails stack, such as out of memory errors.
If we're adding Logentries to a client project, the best solution is to have the client set up their own Logentries account and add the relevant thoughtbot members. If the client doesn't want to set it up or there's too much red tape, we can create a new project on the thoughtbot Logentries account and then delete it once our engagement has ended.
We don't use the Heroku Logentries addon, as it will automatically create a number of alerts and send them to every admin on our Heroku organization.
To set up Logentries for a Heroku application, follow the instructions for setting up a syslog drain.