Wow my 120 days old domain has got PR4 ... I even doublechecked from another place - it does show PR4 ...
I did next to nothing in terms of link building. Here is exactly what I did, in natural order:
1) registered profile in a small forum in my niche, added my site to my signature and did about 12 posts there so far (no spamming, the SUBJ is of my interest)
2) registered another profile in another a bit larger forum (same niche), and had about 3 posts there
3) submitted stupid press-release to PRLOG.ORG, (referring me about 1 visitor per month) but did it for BL
4) submitted my link to the authority .ORG site's resources page, and they approved my link, so I have got another link from .ORG PR3 page, also getting 2-4 ref visits from there daily
5) emailed a webmaster who has an old directory site in my niche, introducing my site and asking for a link, and they added a link from PR5 page, they also send me about 25 ref visitors daily
This is it, I did not do anything else.
In Google Analytics I see 21 different referral sites for the past 2 months. 7 of those are Google.XX.XX (Translate, Images, CO.UK, .CA, CO.HK, .RU, .JP, etc). Also there are 5 sites that I did BL myself.
So there are 9 sites where other people put links to my site. Too lazy to trace them down to see their follow/ page PR
Google's link:mysite.com shows 3 links
inanchor:mysite.com shows 8 links and 6,000+ with duplicates included (almost all are my internal links)
Yahoo's site explorer shows 26 external links from 8 domains