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: 
I would expect that the musicians in top bands play extremely consistently, due to sheer repetition and the fact that it's their career.

However, your question touches on a trickier idea: What exactly is a "mistake"? If the exact notes and rhythms are prescribed, then any deviation from that clearly constitutes a mistake. But how precise does the timing/tempo need to be for the rhythm to be considered correct? What if it's technically correct, but a bit off stylistically or emotionally? What if something is "supposed" to ring out, but the fretting was a bit off and a note got partially dampened?

And what if the music is improvised?

From the listener's perspective: would you rather listen to a solo that was beautiful but had a wrong note, or one that was technically perfect but soulless? Anecdotally, my favorite rendition of a Debussy piano piece has a blatant key signature mistake in it\*, but it's still my favorite due to every other aspect of the performance. My old piano teacher tells a story of performing a section of a Bartok piece in the wrong *clef*, and people still enjoyed it.

The whole idea of perfection and mistakes is not very well defined, and in performance art it must be that way. Ultimately, the question is not whether or not a performance was "perfect", but whether or not it was enjoyable and conveyed whatever it was supposed to.

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\* For the curious: [Van Cliburn's recording of Jardins sous la pluie](https://www.youtube.com/watch?v=m8rXQCewQjA). The section in C# in the middle, he misses B# in the melody each time.
I'll talk about live performances since, as other posters have mentioned, recorded performances can easily be fixed with editing.

Mistakes? Yes. Always.

But don't let them stop you!

As a not-top-notch performer I can tell you that there is a stark difference between your (the performer's) perception of the performance and the audience's. In a band situation, you are concentrating very specifically on what you are playing while the audience is taking in the entire performance of all of the members. Not only are you paying more attention to your own performance, but often there are monitors allowing you to hear your performance more than that of your bandmates. This can make you think "wow, that stood out like a sore thumb", when really it's not as prominent as you are hearing. 

Further, you can feel your mistakes. You feel your fingers slip or not hit the strings with enough force. This extra sense of the mistake underscores when they happen. 

An interesting aspect is that due to the nervousness of playing in public and having practiced a song many times, you are perceiving time differently. A mess-up will feel like it lasts an eternity but typically they are over so fast that it will fly by before anyone gets a chance to notice.

The real key to a good performance: when you inevitably make mistakes, don't let it show. Don't make "I messed up" face. And after a performance, just don't mention mistakes, even though it might be the first thing on your mind.