[quote name='PeteFromCorby' timestamp='1397670080' post='2426326']
Is it not useful to know that every C# is between a G# and a F#
[/quote]
I do know that C# is the 4th of G# and that F# is the 4th of C# etc. and it's good to know the cycle of fifths (and indeed fourths in reverse, and your scales etc.) but none of that tells me where the notes are on the fingerboard.
In fact, once I am playing a certain key, let's say C#major, then I'm not even thinking where is the F# note, I am just playing the fourth because I know on the fingerboard where the fourth is in relation to the root. And if someone were to say to me, 'hey, what note is that?' I'd be as likely to reply 'fourth' as 'F#'.
However, the problem with your original observation is not that it's unwise to know the circle of fifths - quite the opposite, it's very good to know it - but that's not the way to learn the fingerboard.
You might equally as well have said that in standard tuning the bass is tuned in fourths e.g. BEAD at the 7th fret. OK, totally correct, but it doesn't learn me the fingerboard and never will.