Question: I playing guitar since a couple of years (but not regularly) and I always wondered if guitarist from known bands always play their songs/solos perfectly?
Especially when the songs are fast paced, is it easier to make mistakes that no one will notice? When I play solos I am never really satisfied with my performance since it doesn't sound exactly the same like in the song.

I know there is no exact answer but I would like to know what you think so I can silence my conscience :)

Answer: 
'Perfectly': never. 'Very Good': usually. Professionals tend to want to show you what they can do, rather than what they can't; it's their meal ticket, after all.

One of the skills in being an instrumentalist though is to practice techniques that allow you *to* power through small mistakes without disrupting the rhythm or the overall feel of the song, or letting your small mistake trip you up and turn into a bigger one. Pros will generally be good at this aspect of instrumentalism too; it's one reason you may not notice their mistakes.
No. Professionals are so perfect they never hit a single note wrong, and if you try to play like they do and they find out you make mistakes, they will come to your house at night and you will be banned from playing in front of people until the end of your life (or the end of the world, whatever comes first.)

Ok, now forget everything I just said.

Of course they do. Sometimes, it does happen that guitarists (or trombonists, saxophonists, etc.) play perfectly if they practice enough. I myself once scored a perfect score in a contest with my flute solo. And- I've also failed miserably the next year I did it, even though the piece was (sort of) easy and I've played it fine millions of times before. So I know the feeling.

Some mistakes can be covered up, especially if you're not playing alone and you're not totally terrible. And even if you are- if you play a Bb instead of a B one time, no one will notice. Really, it depends on how well you play. Everyone makes mistakes. The difference in levels is that when an ok musician messes up one note, they freak out and mess up even more, humiliating themselves completely; however, when a star forgets a big chunk of their music, they begin wildly improvising something that is way better than what was written. (This actually happened once at a concert with our band; a saxophone player had a solo part, and he missed the entrance by a few beats, so he just started playing something completely random that wasn't anywhere near what he was supposed to play. But it was honestly amazing- after the concert, we all agreed that we liked the new version better.)

So yeah, it happens. There are only two good ways to deal with these situations, however: when you goof up, cover it up with something better, or, as I heard from my band director hundreds of times: "Don't practice until you can play it right; practice until you can't play it wrong." 

Good luck with the guitar!