Rick, while you mention shifts, a question..

Just after the start, with fairly well set marks where no sides give a clear advantage. How large a shift would you accept before you tack?
What about midways to the top mark, and just before the top mark?

This all depends on how often it shifts, other boats, strategy and tactics of course, but I wonder what your experience is?

If it's just after the start, and we believe the shift to last for a while, we tack (if possible, tactics/strategy applies) even on small shifts. We also tend to tack fairly quick midways up to the top mark, be we dont like to tack just before the top mark, so we accept shifts there (unless it makes us miss the layline, then it's just a tactical question).