I don't have one yet and I was wondering if a lot of people used them or not.. and if they did, what they practiced for how much time...
On weekdays I normally just run through scales, improv, and work on songs that I'm learning. This spans anywhere from an hour and a half, to three hours.

On weekends when I have more time, I run through scales, improv, theory, techniques, and then run down my iPod playlist of songs...about 160 songs. I play the whle Nirvana album, Stadium Arcadium(about 15-20 songs), Led Zeppelin(10-15 songs), all three volumes of the Guitar Tab White Pages(20-30 songs each of the 3 volumes), and then random tabs I've printed, or the pillows' bandscores I have.

This ranges from 2 and half, to 5 hours over the course of a day, and I normally do that Saturday and Sunday.
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I don't have a band ( ), so I practice by myself. It's usually:

5 mintues warming up
30 mins - 1 hr playing songs
1 hr chromatic excercises (1234321)
More songs
Transcribing some songs I like

Not all in one go, that's usually what I do in a day, unless I have coursework or something else important to do. Happens too often
I schedule it with my tv. I play from 7-8 pm while scrubs is on and then from 9 to 12:30 (depending on what's on)
"there is a man...
playing a violin...
and the strings...
are the veins in his own arm."
i reckon during the week about 4 hours of playing, then about 8 hours on the weekends with my band. And its not like theory or anything, just the excersises, playing out set, making new material.