I love iPeng, the plugin and versatile iPhone remote app for Squeezebox players – the extensive range of features comes with with the price, though. iPeng is not the most simple of players. It took me some time another day to debug a little problem, for example: iPeng appeared to be stuck on repeat. Songs I added were included in the playlist, but player would not move forward. A single song would only repeat. It took some time to find where the repeat setting was: you needed to tap once the play (cover view) screen, after which further settings would be revealed, including a symbol for controlling repeat settings. Repeat to off, and the problem was solved. – An example of more ‘expert’ style app/interface design than what I consider desirable today — great to have this level of control, on the other hand (after you have done your homework).
frans goes blog 
For more lessons, here is the link to iPeng user guide: http://penguinlovesmusic.de/ipeng-the-iphone-webapp-for-squeezecenter/users-manual/