This is an impossible question to answer fully. It isn't so much THAT you do exercises, but rather HOW you do exercises. Merely playing scales isn't going to do much for you.
Having said that, I do practice "scales" daily. I may use some of the five patterned scales that keep the hand in one position, or I may connect them adding shifts. Or I may do chromatic scales. Often, I do various patterns on one string, a pair of strings, or all six strings. Sometimes I incorporate small shifts, or large shifts. What is important is that the patterns make use of all of the fingers, and are easy to memorize, or are deeply ingrained. Learning scales and patterns is important, but is a completely separate exercise. To work on speed or any technique, you must use patterns you know very well so as to give your undivided attention to the task at hand.
I spend a great deal of time playing slowly. Similar to what I stated above, playing slowly in and of itself isn't going to do much of anything. Rather, it is the vehicle from which I work: to refine movements, to use less energy, etc. Fast practice is equally important, but only if the ease of movement can be maintained. Speed can be pushed in short bursts of few notes. What is learned can gradually be applied to longer scale passages.
Dr. Todd Tipton, Noda Guitar Studio
Charlotte, NC, USA (available via Skype)