'Dump stats' are generally 8 in the modern D&D incarnations, which is not a number to be sniffed at. It is only marginally less than average and barely a 'dump' stat at all. This can change if your racial build has a penalty to the same stat, of course.
I've been at tables where players had characters with 3 or 4 in a stat. This was usually in the days of rolling and reallocating on a 1:2 basis (so you could lower your rolled 12 by 4 to increase a 15 to 17 elsewhere). CHA was the one that used to frustrate me the most, because players used it as an excuse to play arseholes. INT was another one, of course, and I've players making ridiculous and disruptive decision 'because my character is really stupid'. Attacking the Emperor as he hands out the quest is just one example I can remember.
All that said, I've seen some good RPing with characters having very low stats. Like most character-developing mechanics, it all depends on the player to make it work well.
