Originally Posted by: dfarisI guess that reason gets thrown out the window when playing some exotic scales that mixes it up;like when u get an F and a F# in the same scale.[/quote]
Yes, there are times when it is unavoidable.

However, even in cases like this you can do double-sharp or double-flat if it helps clarify the letters used in a scale. Typically the only situation in which you'd have to use the same letter more than once is in a scale of more than 7 notes. Because there are only 7 musical alphabet letters to use!

So in your example you could use E-sharp (for F) and F-sharp. Or use F and G-flat. Or use F, G-flat and A-double flat (for G). There are many options.
[QUOTE=dfaris]There are so many ways to play 1 scale in 12 frets.
I dont know if I should learn them all, or if there is a most popular one and the rest of them are just finger excersises?