As always, great insight and information Mardelin!
Breeding mother to son is NOT linebreeding, it's inbreeding...BIG difference, BIG no-no. Some well-seasoned breeders will line breed to bring out certain traits in dogs, but it is certainly not something to attempt if you have minimal knowledge regarding canine genetics. More and more it seems, claiming that a dog is "line bred" seems to be nothing more than a facade used by BYB's in an attempt to justify unethical breeding practices.
I can assure you, contrary to the prior claim made in this thread, reputable breeder, whether they show or not, do not purposely breed mother to son EVER, much less "all the time." I believe that julietimothy has provided a very good example of what can result from inbreeding one dog to it's offspring.