I love how their first suggestion is upgrade your db $$$ .
Performance being shit would be fine if it wasn't a miserable experience trying to migrate off. Not being able to setup replication to slaves off of Heroku means you have to deal with things like Bucardo and all the problems that brings along.
Heroku is really awesome for little web apps that performance doesn't matter on. If you think you're building something that people will want to use, you don't want to be on Heroku.
Obviously, you need to deal with backups and that sort of thing, but, you can hire a full time person for the price difference between Heroku and EC2 as soon as you get to the top end of Heroku pricing.
It was posted about quite some time ago: http://orion.herokuapp.com/past/2009/7/29/io_performance_on_.... If this has become bad advice, inquiring minds wish to know. EBS Priops seem promising and different.
Replication out of Heroku would be neat, but the WAL as-is is architecture and operating system dependent. Luck and tenaciousness willing, logical replication in Postgres may yet serve that use case, some day -- we'll have to see as to the details. A lot of effort has been expended attempting to get it in some form into 9.3, but it's far from sure thing.
Also, don't forget to set up archiving, if you continue to retain fast interconnect with S3: https://github.com/wal-e/wal-e, which I principally wrote on Heroku's behalf, but now is a project of multiple users and contributors. It has a focus on ease of use and reliability, although it could suffer improvement.
Either of those options would have been awesome (anything but Bucardo, really. Bucardo's triggers overwhelmed an already overwhelmed database)
We run many busy PG databases on PIOPS. The difference from normal EBS is huge. Very happy with PIOPS.