One question that comes to mind is regarding whether or not Kraken plans on implementing a quality live stream data platform.  If Kraken wants to compete with Mt. Gox, they will need a data streaming platform much like Clark Moody's site (http://bitcoin.clarkmoody.com) along with advanced candlestick charting across multiple timeframes (perhaps integration with SierraChart via a websocket-like feed from BitcoinCharts).  If Kraken has good APIs & succeeds, perhaps 3rd party programmers will develop a solution as well.

I also am interested in what kind of trade history would be provided, if any (unlike Mt. Gox's trade history which breaks them into tiny orders rather than providing the lump sums with average costs, and fees broken down accordingly).  Quality trade history that is easily exportable for tax accounting purposes would certainly be beneficial for some people.