Having used WordPress on and off for a number of years and only recently jumped on the iPhone bandwagon it was more or less a given that I had to try the WordPress iPhone app. The app is very easy to setup and supports multiple WP blogs.
Convenience for being able to blog wherever you are does however come at the cost of several core features. Realistically though I doubt you’ll be churning out novel length posts this way but it does have some uses for basic admin tasks and micro-blogging.