Unfortunately, we don't have quantified numbers on that, other than knowing that a study was done in the year after the capital gains was completely lifted, and the number of gifts of securities doubled and the value of those gifts far more than doubled.
Anecdotally, in my own experience, until the economy took a downturn and the tax advantage of gifting by securities became less attractive, every organization I'm involved with or have worked with—and across the board—was seeing increases. I know that for our local United Way, their campaign goal in the year following was somewhere in the vicinity of $46 million that about 40% came through gifts of securities. In the previous year, it had been less than 10%.