I used to play from 4 to 10 hours a day when I was in school and college. Now that I have a wife, babies and a job I never get a chance at all to 'practice', when I do get a chance to pick my guitar up (about 4 hours per week) I cut to the chase and compose. Once you can shred you never forget how, I actually improved more when I stopped playing as much. I think the longer you've been playing the more you realise you don't need to keep playing scales, that's when you actually start getting more out of your sessions. Practicing scales etc is a waste of time, once you know them that's all that counts. Staying away from practicing scales and runs helps me to get more creative as I have less of a tendency to get stuck playing the same up and down stuff that a lot of guys do. It's wierd, but I only got 'good' once I stopped practicing as much and started listening to how 'great' players compose (Jason Becker, Vinnie Moore etc) rather than trying to emulate their techniques. Just my 2.5 cents