Installation and configuration of apps should be trivial - just run App manager, select you app, install and go.

Most of the (complicated) discussion on here is about customising bits that Nokia weren't really expecting people (and other platforms make it impossible) to customise. At the moment it's still at an early stage, with people finding new bits and pieces to tweak (and occasionally bricking their N900s in the process). Eventually, I'm sure, there'll be apps written to simplify this whole process and make it trivial for the end user to do this themselves.