The new combination speedo/tach is BRAND NEW this year in the big wishbook, which I picked up last weekend at my HD dealer. The combo units have been available for the bigger bikes, but for the Sportster it is new for 2009. The unit only works on 2007 and later bikes (obviously those with fuel injection). The 2007 bikes require a special resistor interface to work. 2008/2009 is plug and play from what I have read and talked to the service techs.
I doubt anyone has experience with this unit yet, as it just too new. However, HD is VERY competent with their equipment, and it pretty much always works, and works very well. I wish they could make it work with my 2006 model-I'd have one very quickly!
My only choice is to add the separate unit, which is fairly easy to do (about a 3 hour job from what I have read). Maybe someday, but for now-my ears, hands and feet are still serving me well, just as they did for years of MX racing.