Hm. Well usually the individual page that your article is listed on an article directory has pretty much zero page rank...and those account for most of my back links and my site is currently PR3.
One also has to remember if you have 1000 PR0 link exchanges atleast 80%+ will gain some kind of PR. As far as indexing that all depends what the site is and how the site owner is promoting the site and or putting fresh content on the site. There is more to it. But I would have to say it does help some. The rest really depends on you.
Certainly it helps. In the next update, that may gain some PR. But if you want to do link exchange then you have to be a little careful there. You need to check some factors like, the sites are not too old. If it is an old site then there might be probability of penalizing by the search engine. As long as you are going for one way linking, it is safe. But try to avoid getting links from irrelevant sites, if you are seeking a good number of organic traffic.