Santa Rosa? I worry and wait. This late, definitely.
Basically its going to offer a faster FSB, faster RAM, NAND caching (makes computer feel more 'snappy', saves power), faster integrated video (personally I don't care, but this will be very important to some), and some power/battery run time enhancements.
Its unlikely to introduce bugs as its an upgrade to Yonah, rather then a whole new core. In fact, it will probably reduce the amount of bugs.
But Santa Rosa is only part of the story. Newer graphics cards will probably be simultaneously be included. Think 8600 or X2600, probably resulting in a ~50% performance enhancement.
In other words, it would be very silly to buy now. Silly and costly in resale value.