All right, here is a digital example
I have been to several events where the DJ has had nothing but a Macbook, an iTunes playlist and a really good set of speakers. I have spent several hours at these events listening to digital music I did not pay for.
Here is another example. I have visited my techie sister and mucked around on her computer while I was there. She let me look through her ebooks. Most of them did not interest me (she reads a lot of erotica; I do not) but there were at least two that I read in their entirety on her Palm organizer while I was there, and there were a handful of others I might have otherwise bought but I browsed for long enough to know they weren't my thing. Those might technically be 'lost sales.' But then again, I could go to a paper bookstore and browse a book there and decide not to buy it, so this is the same thing.