It's normal. It was happening to me as well on March. From PR 3 to 0 but my SERPs are improving so I never complained. You will complain if you provide "paid review" or other forms of paid links but I don't.
it is not waste of time, PR helps in making money online (links, reviews)..that's why I think people are concerned about it..
No it is not a blog, domain age is almost 3 years. PR was 4 last year then it dropped to 2 last year and then campe up to PR 3 this year.
Can be, because if I do Link:www . mysite then I see less links than before. If I go to Google webmaster tools then I see 6oo links and I had over a 1000
Google is a sick, evil and twisted company. The sooner webmasters learn to live without Google the better off everybody will be. Let's face it. Google is not a webmasters friend, they are the enemy. Google will cheat you out of your Adsense earnings at the drop of a dime. They say they don't allow MFA sites but they have "Adsense for parked Domians" which is worse than MFA sites. They will cheat you in Adwords if you don't watch them closely. They save all the email you delete in Gmail and Analytics is just another spyware tool to invade internet users' privacy.
Whatever you say, Google is still the source of my traffic. And guess what? The conversion rate from search engines is 10x better than from social media sites. If you try to live without Google, it means you want to get less income. That's all. Yes, they are evil but I won't complain as long as I still rank highly in my targeted keywords.