Well, as I understood it the queueing happens in some kind of load balancer that is responsible for routing the requests between different servers ("dynos" in Heroku speak) to handle the requests. New Relic is a plugin for your server and hooks into Apache and PHP (or this case Rails) to learn how long it takes to process the requests (and retrieve data from the database and/or a cache). This means, to me, that queueing strictly is out of the scope of what NewRelic normally does.

However it's great that they and Heroku now found a way to report the correct queueing time. As far as I understood it, they use a special header added by Heroku to calculate the time themselves and report it in their dashboard.