CDC has just updated its estimate of cell only households from the National Health Interview Survey. For those of you not paying attention, this is pretty much the gold standard for tracking the growth of cell only households. CDC now reports that as of June of 2009, 22.7 percent of US homes have at least one cell phone but no landline. 
Another 14.7 percent report having a landline but mostly using their cell phone(s) to place and receive calls. Putting the two together, this means that a standard RDD telephone survey is likely to miss about 37 percent of households unless it is augmented to include cell phone sample. While it adds time and expense, calling cell phones is rapidly becoming a standard feature of US telephone surveys.
I'd like to find a silver lining in this but can't.