I've got the basic Dice module in my E36. Honeslty i've yet to come across an interface that's as good or responsive as the actual iPod itself so I prefer to control it directly rather than remotely. The intravee looks pretty tempting though as it seems to make the OEM headunit as intuitive as it possibly can be.

Not sure what i'll do for my X yet though.. the basic $40 aux input plug is tempting because of its cost & simplicity! I'm not in love with the Dice for what it costs comparatively.