Here's the timeline.. 16 visitors in July 2007 and broke 10,000 in March 2008 so less than 10 months. As for other methods that "helped" were stumbleupon, link exchanges and blogging comments with sites with a pr of 8 and higher.
To bring it inline with my other favorite article sites, how many free PR sites do you think we need? how many do you think the search engines feel they need to determine a sites value? right, probably only one or two, duplicate press releases across a bunch of sites is the same news on 10 different television channels, or an article posted on 400 article directory sites....USELESS lol (yes they build some low value links and incremental traffic which wont pay hosting ) Another issue people need to remember is there are 1,000,000,000 sites out there, and what works for someones very low competition niche, may not hold true for someone marketing online gambling....
Personally I think the only site that you need is going to be the prweb and after you complete a successful release it will get picked up by many other sites at least that has been my experience so far. That being said, as long as you do your research on your niche and keywords you should be able to figure out what is going to be profitable for you in the long run.
I know that DP doesn't do much of anything with social bookmarking anymore but for those of you that liked this post.. you might find this link http://seotips4free.blogspot.com/2008/03/150-social-bookmarking-sites.html helpful if you're looking for a good list of social bookmarking sites.
Your point about having realistic expectations is quite pertinent when it comes to SEO and internet marketing. A little initial research can go a long way. One should be informed about their niche and accurately evaluate the competition before taking the plunge.
We have press released among out 20 free or low budget lead generation ideas... but I guess it is more important test every method for every specific business.