skrbl: a Web-based whiteboard

skrbl looks to be the newest entry into the virtual whiteboard space. It joins Imagination Cubed from GE, and Thinkature and there most be others as well. This doesn't even get into the number of online, collaborative writing environments we now have. At this point, at with no disrespect intended toward the creators of skrbl, one does have to wonder if this is just  a race to be bought - one can assume that Google, Yahoo, MSFT will all be needing virtual whiteboards to add to their online office suites (if they don't already have them). Also, what could be the sustainable business model for a stand-alone whiteboard? Just wondering.