Once I did that, I looked to the keys that were the most similar to Key of C; Key F & G. They both only have one note difference from Key of C. So since I knew Key of C by heart, it was really easy to get a hang of those two keys because I only had to alter one note from what I already knew.
On top of that, I learned that all the patterns I learned for Key of C, I could simply shift the patters on the fretboard up or down to get into a different key. A good visual example can be seen using this virtual fretboard:
http://www.all-guitar-chords.com/guitar_scales.php
Click and choose C Major. Then click onto C# Major, you will see that the patterns simply shifted up one fret. So in a sense, once you learn one key by heart, you'll know the rest.
How I learned the Key of C, was I memorized each box pattern:
http://www.i-love-guitar.com/images/guitar_scales_major_printable.gif
You can actually argue that each of those patterns is a mode. So, the mode patterns if you will. The first pattern displaying Phrygian, the second Lyidan, than Mixo, etc.