Thanks for the replies. The lag varies with the type of yeast, some seem ok, and some seem to take a full day or two to get going. I am doing 1 gallon batches by the way. One type, I think it was Safbrew T-58, produced very little activity the first 2 days, and then quit altogether. I roused the yeast by gently rocking the closed fermenter and it soon began bubbling through the airlock again. I may be worrying too much, as the beer turns out pretty good, but as I am new to this, I just wondered what other brewers were doing. The books I have read (The Complete Joy of Homebrewing and How to Brew) recommend rehydrating; I had not considered pitching it dry, maybe I'll try that next time.