The winds hammered us out of the northwest for four days, dropping the temperature to seventeen degrees. The buds had just broken two weeks to0 early, ushering in a period of prolonged frost worry. But by April 9, the worry was over. The primary buds, many of which had turned into one-inch shoots, were dead on most varieties. This photo is of a freeze-killed traminette shoot.
Many growers lost everything. I'm still experimenting at this point. My commercial vines won't get planted until Spring '09. I won't have a crop until '11 or '12. But for those growers for whom this is all they do, it's going to be a tough year.
Below 22 to 24 degrees (F), young buds and shoots will sustain damage. Fortunately, the vines probably not die. It's possible that, once the sap starts running, trunks and cordons can sustain damage they'd otherwise be able to survive in the winter. But it's not a certainty. If the vines died, that would be truly disastrous, growers would be set back years rather than simply lose on crop (and possibly impact the following year's crop as well).
Some folks will get a crop. Each bud is actually a packet of three, holding two buds in reserve for just such an occasion. But the secondary and tertiary buds are usually not fruitful. Some hybrid varieties can actually sustain a solid secondary crop, but it's not common.
One grower recently said that it's time to start looking to the '08 crop. It'll be a long wait.
More info on the cold snap.