I hear tht the guy from trivium had to practice 8 hours a day to get to his level of guitar playing an slash took twelve!

do you think this is true?

do you think so much practicing is necessary to get good?
I seriously doubt you can get anything done when you practice so much that you only have two hours to eat and do other things.

So no.
Going to Columbia University this fall! Woohoo!
Member of UGPSA: Ultimate-Guitar's Potsmokers Association
it all depends on how you use your practice time really. 8 hour practice sessions are not uncommon depending on how much you want to work on and how long you want to work on it and if you are going to be doing speed drills with each. The more you get into guitar the more you can have to practice with. You have stretching and warming up, then chords, scales/ modal theory, application of music theory, arpeggios, picking styles such as economy or alternate(depending on which you prefer). You have your techniques like Tapping, sweeping, hammer on's, pull off's, slides, bends, harmonics(both artificial and natural).

Thats just a sample of what you can have in a practice session, but I tend to break all of that up into two days sessions, do these on day one...do these on day 2, then repeat. Usually doing about 4 to 5 hours a night if I can. Not everyone is going to use all of that though, as players varie in not just skill level, but style. Like sweeping might be something I use, but another player might have no use for it, thus no need to include it in their list.

The main point of practice is just what is says though. You are PRACTICING these things, this is the time when you take it easy and get the fundementals down and work toward upping your skill, your not just jumping in and playing everything as quickly as you can, but slowly building up to your level and then trying to see if you can surpass that, then if you can't move back down and start over. Practice time is to better yourself not show off, so use it wisely and take your time on the things you want to work on. If I'm doing speed drills I'm not slamming out 16th notes at 192bpm I'm starting around 100 and slowly increasing until I reach my target goal. I might play a lick 10 or 15 times accurately before I decide to up my bpm.

I make sure each note rings outs clearly, that both of my hands synchronized and that my finger frets the note as my pick picks it. When doing theory I go through the application slowly and name out the notes I'm playing, I'll name out intervals I'm hitting. and I make sure to use a metronome to make sure I'm in time rythemically.

Does everyone do this....hell no, but thats an example of how some people can have those ungodly practice times, it all depends on how much you work on and how much you really put into it. No matter how much time you put into your practice session or what you practice, the main goal is accuracy, you want to make sure what you are practicing is coming out accurately and that all of the mechanics behind your playing are being accurate.
Quote by Shredlet
Cheers Sinister that was really helpful a Dime-point to you!

"Any problem you can't solve with a good guitar, is either, unsolvable or isn't a problem."
Well lets sum it up quick for you.....
If you dont practice you wont get good,
therefore: practicing is necessary to get there.
dont forget these guys get paid to play so instead of going to work they sit and play,
Lucky bastards!
I can tell you the secret of anyone that practices for 8 hours a day (or more):

It's not obsessiveness and it's not a lot of boring work.

They enjoy it because they know HOW to practice. They have seen that
really focused practice and awareness of what you're doing results in totally
amazing progress. When you get a lot better at playing, the actual work
of getting better becomes very enjoyable and fun.

The single most important thing you can do as a guitarist is learn HOW to practice.
Everything follows from that. If you're bored after a few minutes of doing scales,
you certainly do NOT want to spend hours doing that and hating it. It won't do
you much good anyway.