My personal thought is. Yes its a total waste of time / energy and also waste of traffic. I like to have my articles on my sites / blogs / forums so whatever ranking it generates out of it comes to my site and not to some scrap site.
u'r site in some ways, BUT if u submit ur articles on directories, u get noticed by ppl, and they make sure that they be a part of ur website by clicking on the link in ur signature or ur profile. so that helps.