It's not a nice experience: portrait mode only and iPhone/iPod Touch screen size which becomes horribly pixelated - inc. keyboard - when enlarged.
The WordPress app offered a much nicer writing experience (see my Twitter blog for an example). I could also insert pictures with the WordPress app - I can't with iBlogger.
So, the app works fine on the smaller Apple devices but is much less satisfactory on the iPad. It needs an upgrade desperately - the TweetDeck iPad app leads the way in this respect I think. iBlogger 2 is due for release soon - here's hoping it's more iPad-friendly.
Mobile Blogging from here.