This happens just 4hrs ago after March 30 ends, and my traffic starts to fall like a rock.. Is this the effect of PR updating or my site is totally removed from being indexed.. Please enlighten me
Your website is still indexed. You can do a site:<site> command and see all of your indexed pages. It might be worth seeing if Google Webmaster Tools gives any warnings about your website. You should check your website's logs or analytics to see where you are losing traffic from. Perhaps you have lost most of your Google traffic or perhaps you are losing traffic on only certain keywords. It could also be a result of losing traffic from yahoo or msn. Your website is very new though. It is very common for a new website to have unstable rankings. Many people believe that a new website often ends up in the Google sandbox shortly after Google first indexes it. Apparently it can take a year to get out of the sandbox. If I were you I would just keep working on your website as normal...keep adding more unique content and keep building more quality backlinks. In time you should get that traffic back. If you were doing anything spammy, stop doing that and remove anything spammy from your website.
I noticed this too, it is probably another SERP dance, like what we were seeing last month. For me, i dropped from double index position 1 and 2 to single index position 30 about the same time that you report seeing your traffic drop. Google is working on their database (most likely) and things will settle down in the next week or two.