The advertised features are amazing. Unlimited hosted domains, e-mails, and MySQL as well as lots of disk space and bandwidth. Also has good control panel tools for setting up domain functions and new databases. Support gets back to you in a day (although they won't always solve your problems).
Our website, however, is slow most of the time (we have confirmed this is a problem with DreamHost). Also, half the time, their control panel does not load and we have to use it later in the day.
Their PHP configuration is very strict. Three times we had problems installing standard scripts because of this, and they refuse to remove their restrictions.