It may be true in the normal people market segment that it will increase sign-ups, but it's absolutely not true for me.

Admittedly I'm not normal, but it might be considering the market at which the site is aimed, and the type of people you're trying to get signed up. I have significant disposable income, and actively look for ways of trading that money for either time or knowledge. Having that modal pretty much guarantees I won't be back.

So ask, it might increase number of emails in your list, but will it increase your income?