Ive recently adjusted the truss rod on my Epiphone Les Paul-100. I was getting a lot of buzz, so i made the necessary adjustments, and all is fixed now. However, i dont have an EXTREME amount of bow, but its noticeable. I dont think its too much as it is now, but how much is too much??
Hold down the low E string at the 1st fret, and also where the neck meets the body of the guitar. Should be around 15th -19th fret. With both of these held down, look in the middle of those two points, around the 7th-9th fret.

If the gap between the string and the top of the frets is more than a credit card, you've got too much. You generally want it as low as possible without resting on the frets. About enough to slide a sheet of paper through.