Not sure if this is already known or if it is a new feature, but I just updated the Kindle iPad app to v2.5.0.37 and it allows me to drop non-DRM Mobi files directly into the app via iTunes. Is this a new feature or could the app always do this?
I was under the impression there was no easy option for reading Mobi directly on iPad, but with this Kindle app update it seems there is now - at least, for basic reading/annotating it's probably sufficient if users don't wish to convert to ePub via calibre, etc.
I still will purchase ePub whenever possible, but at least it provides a good option now - good news (for me anyway)!