Does Tor usually give issues when basic browsing? ie. not super user stuff, basic average internet user stuff.
In my experience, what people have trouble with are services offered by Google. I don't mind it myself, there are other search engines and I don't use any of their other services. Also, captchas can be annoying. Generally speaking, it really depends on what sites your using.
If he is not doing anything illegal why would he cares who sees what he is doing? Besides hiding from ads on Pandora, which doesn't work in Tor btw.
I can't speak for your friend. You might just want to ask him about it. I also use Tor Browser most of the time and I haven't ever used Tor Browser because I wanted to do anything illegal. So, I guess your friend and I might have similar reason for using Tor.
There are two main reason I use Tor:
a) I don't know what information I want to have hidden in the future. People that opposed Women's right to vote 40 years ago might not want this fact to be known publicly today. Times change, and so does what is accepted by society and governments.
b) I'm one of the lucky people that does not depend on Tor. However, there a people that do, activist and journalist for instance, and they need strong security. These people depend on others for one simple reason. If only people that have something to hide use Tor, they become very easily identifiable. Let's just say a politician attempts to overthrow one of the government leaders. He obviously can't do that alone, so he uses Tor to communicate with his associates. If no one else uses Tor or any other secure commutation, they can not communicate anonymously. This because the only ones whose communication can't be read, are the people you're looking for. Frankly, anyone depending on Tor's anonymity depends on people, like your friend, that ensure they can hide in the crowd.
I he wants to prevent his computer from learning what he is doing incognito works too... as far as I can tell.
Can you elaborate on this a bit, I'm not exactly sure why you would want to hide something from a computer.
How sure is the entire Tor community that Tor is 100% anonymous, …
Tor is decentralized (not controlled by a single entity), able to provide security updates in a timely manner, has been well reviewed, … and so on. This is far more than most anonymization services/software can say. Nonetheless, it certainly is not 100% anonymous and the Tor Project is aware of this. However, if you don't use Tor, there is nothing protecting you. If you use Tor, you may be identified, but this is certainly harder and who ever wants to deanonymize you has to be willing to spend some effort (and money) on it.
… it was designed by the US Navy how do you know the NSA isn't looking at people on the list, maybe you are not on the list?
The source code of the Tor Browser is publicly accessible and you can verify that your browser matches the source code. Also, most people use Windows or Mac, I can't see how it is harder to get a backdoor in there. An OS is far more complex, involves more people and the source code in not publicly available. Not saying they have backdoors but why would you try to get a backdoor into Tor when there are easier targets. Also, what list are you referring to?