Yes it is true that PR is not Important but PR of website increases when people starting to refer your website and that also help to increasing traffic. thats why website like wikipedia and facebook has high PR. But the most important thing is content. If your content is original, unique and useful for people then automatically you get all these things.
This happen also to me, my website get 5 pr suddenly but after some time it comes down on 4 pr but I think PR is not important but rank om search engines Matters.
Wow, awesome.. Can you restore what you did in this two months? You have backlinks to site?traffic? your site is web 2.0?