A 3" lift is getting close to the fatal angle...there's really no solid line of demarcation. Some say you can go to 3.5" before your front ds will be at too much of an angle. I've read of folks who got 3"+ of lift and had no problems, and others who wound up with a seized ds. It could happen after a month, a year, or never.
My advice: If you go 3", don't worry about the driveshaft; if you go over, I'd buy a new one. If you decide to buy a new one, you'll want a 1310 JE Reel, Tom Woods, or Coast.