Any friction will ultimately affect "conversions", although I think the friction is probably smaller that we'd think. Most people don't spend much time reading and fretting about the TSA online, so for those, standing in line for half an hour and having your passport stamped is just part of the excitement of travelling (for less experienced travelers). As a fraction of the total time and bother of intercontinental travel, it's almost negligible.
"Most people don't spend much time reading and fretting about the TSA online"
That's only true for countries under the U.S. Visa Waiver, which are maybe 5% of the world's population (basically European Union and Australia).
For the remaining 93% of us, we have to think long and hard and plan far ahead before visiting the U.S., and that means being aware of all the issues or risk deportation.
http://en.wikipedia.org/wiki/Visa_Waiver_Program
And yes, I believe it does affect conversion significantly, but, coincidentally, we're the poorer 93% .
Sure - but the visa madness predates the TSA/terror madness if I'm not mistaken?
Yes, but it was much easier before September 11. Uruguay was in the Visa Waiver program back then.
"Following the September 11 terrorist attacks, the George W. Bush Administration decided to tighten entry requirements into the United States"
I ended up visiting anyway (I really wanted to research Philly Cheesesteaks, Maine Lobster and see the colours of the New England Autumn/Fall), but I definitely thought long and hard about it and was apprehensive.
I also made sure my medical travel insurance was solid.
Now, maybe I live in a paranoid white-male bubble that reads about this stuff, and that informed my apprehension, but I personally think it would turn off many, many people from visiting.