I've read many replies etc but i'm not getting it. So basically external nofollow = don't waste my time posting?
Even though they don't pass link juice, consider this: Any natural/organic link development, will have some nofollowed links. Just as some links will have no anchor text and just a URL. I would not avoid nofollow links all together. Consider how Google looks at a site's link profile and if it looks natural or not.
i still wouldn't waste my time posting UNLESS i wanted to anyway. a lot of people tend to go on blog rampages purely for a few easy backlinks.
External nofollow = nofollow. Don't waste time, if you are building links for PR love. For traffic it's does not matter, whether the link is follow or nofollow.