Hi Steve and Randy,
The new Serenity does have that extra tail fin - I'll ask our graphic designer to add that to the website too. It basically looks like one of those small freestyle fins. The tail fin adds quite alot of tracking stability. When it comes to jibing or tacking, the new shape is actually much easier to turn. The nose has a rounded hull shape instead of a sharp spine that is on the 2008 model. This sharp spine made the 2008 model pretty hard to push through the eye of the wind after a tack for example. The new one, because of that round hull shape in the nose, goes around the eye of the wind alot easier: it doesn't catch.
The other big difference is in the feeling of power when riding the new the board, which comes from the extra thickness and more power-orientated rail shapes under your heels. The new Serenity is alot more powerful and that feeling combined with the extra tracking stability adds up to make the whole package faster more exciting to ride. It's still one of my favourite boards in the range.