I am currently subclassing UIView to create custom objects, they work perfectly fine
In interface builder i drag and drop a uiview and I set the class name to my cus
I've researched this myself a while back, as far as i know this is not possible using the iPhone SDK. When developing for the Mac SDK you can create your own IB plugins.
You need to add the custom view to the Interface Builder library. Go to File -> Read Class Files... in interface builder, and select your header file to add your item to interface builder's list.