If Bryan Adams is an example of the way your playing turns out if you play until your fingers bleed, I don't think I'll bother. Maybe that was his one and only practice session? :D

callouses are one thing, but I've got 2 mates who can no longer keep up their pro schedules as a result of excessive practice / OTT speed drills = tendonitis. Just make sure you know what kind of pain you're experiencing....