I just finished pushing out an application to Heroku. I plan on the traffic ramping up sharply along with a couple of slashdottings, HN's and reddits along the way. It gives me a warm fuzzy feeling when I realize I can just "Crank up the dynos" and go have a beer.
Don't forget to crank them down when the traffic is over. There's no refunds for accidentally leaving 1000 dynos running for a few hours longer than necessary.
If/when I actually deploy something worthy of traffic I plan on incorporating something that automatically scales my app, both dynos [1] and workers [2] (up to pre-defined limits, of course)
Don't forget to set your headers - Heroku uses Varnish on the front end so you your app may not even be touched (and hence no extra dynos needed) in a lot of cases.
