I'm curious what your thoughts are on custom objects. I just ran into this article:
He makes some strong points. We have an internal API that we use with Marketo which utilizes custom objects, and we certainly have run into some of the stumbling blocks he points out. I'm hoping that Marketo will continue to develop this feature to a point where it is more usable. What do you do to store/display large amounts of related information when individual data fields aren't necessary?