I'm working my way toward it and I have to say that i've improved immensively. You can also check out Speed Kills by Micheal Angelo Batio or Speed, Accuracy and Articulation by Vinnie Moore.
Play a scale in 3rds,4ths 5ths, ascending and descending. That'll help your speed. The 2 best ways to improve speed are a metronome and patience though.
Pure technique work is very important, and spending time breaking down exactly where your mechanical weaknesses are and designing drills to target them is of course a critical part of growing as a guitarist.
But, the older I get and the longer I play, I've noticed that my playing tends to be better (like, musically better) when I'm practicing things I'll actually use, rather than pure technique drills. Something I've been doing a lot of lately is taking a drum track or click track, picking a scale, and "improvising" in it, accompanied by nothing other than the click, but focusing on keeping my rhythmic grouping consistent. I.e. - playing 16th notes in C minor, but not sticking to a single scale position and instead moving freely around the neck. This has (I think, anyhow) made my playing much more fluid - rather than building tremendous amounts of speed in one position, I've been building better speed and control moving around positions and extending scale runs through wider ranges, both picked and legato. I've found it really helpful.
variation! Scale exercises do get boring, but try to mix up scales with arpeggios. Approach the scale in different ways. Use a line from your favorite solo and practice it in all keys. This will make it much more fun.
When chromatics get boring and you want to mix things up try using the whole tone scale 3 note per string pattern ascending/descending, then move it up a fret, and repeat until you run out of frets.
Michael Angelo Batio, the guitarist from the group Nitro who played the four necked guitar:
Made three instructional films, Speed Kills 1, Speed Kills 2 and, Speed Kills 3, that are really worth the effort of hunting down, he uses scales to teach you both scales, how to play fast, how to improvise with scales and build up finger strength and dexterity.
Speed alone isn't everything.
Controlling your picking is the key.
I'm doing rather odd exercises using only 2 strings, strictly alternate picking.
Picking is always up-down...
2 notes upper string and 3 on bottom, 3 notes on upper and 2 on bottom
1 note per string starting either from upper or bottom
1 note upper string and 3 on bottom, 1 note bottom and 3 upper
1 note upper string and 2 on bottom, 2 notes on upper and 1 on bottom
every odd combination you can come up with, and with string skippings added, basically never play the same amount of notes on the 2 strings...
1-2; 1-3; 1-4 --- 2-1; 3-1; 4-1
2-3; 2-4 --- 3-2; 4-2
3-4 --- 4-3
and work with metronome, aim to raise your speed between 2 and 5 bpm per day.
the most important thing is not only speed, but the stamina to support the speed you want to reach, probably you can play bursts but not be able to play consistently
another thing is...alternate pick everything, alternate pick the arpeggios of ballads, slow down sweep arpeggios and alternate pick them
look at how Petrucci plays Glasgow Kiss...he could "sweep" some part of the phrases, but he keeps his alternate picking consistent.
keep in mind that the fewer notes you play on a string the harder it is to be fast