Pretty cool, but iPad + Paper + stylus has almost completely replaced physical whiteboards for me. The ability to save/send/flip thru drawings is a killer feature that physical whiteboards can't deliver.
The real killer for me is still the lag. Handwriting is just painful, although perhaps simple diagrams are not so bad? It seems to me that an Android tablet could distinguish itself by providing both very low lag with something like the Wacom accuracy. The iPad is unlikely to ever reach the ideal 1 ms lag -- I suspect the retina displays have relatively high response times (but have no evidence).
I find handwriting with my fingers to be a bit unnatural, unfortunately; it tends to break my flow.