Normal people use Tor, for various reasons. You might want to help the Tor network grow. (In fact, the very easy-to-use Tor Bundle means you can also run it and/or use it, without understanding anything about how it works.)
Anyway, I had been running a Tor relay node for a few months.
Friday, I was waiting for a package to arrive. I heard a knock on the door, much louder than you would expect from a delivery person. I went down steps (still in my pajamas, as I was working from home), and saw four Men in Blue at my door. I opened it and was told they had a search warrant for my house. They put their battering ram down, and my girlfriend and I were asked to wait outside while they did a preliminary search of the premises.
The search warrant contained as evidence of probable cause one hour-long IRC chat session (showing origination from my IP address) with an undercover NY state trooper and a perp who claimed to have a boy kidnapped and locked up, along with pictures and videos.
From this evidence, they took three of our digital cameras, my two laptops, two desktop computers, and two external harddrives. They could have taken more, but I think it was pretty clear to the six officers that searched our house that we were not involved.
They said they would get to it as soon as possible and return our property, but sometimes the forensics office has a backlog (of up to six months!).
I guess this is what they mean by "Freedom isn't free."