Did you loose your ranking or just PR? Who cares about PR!!!??? High PR doesn't guarantee rankings! Worry about being in the top 10, once you see the traffic you'll stop caring about PR.
Most people don't know when the next pr update will occur this is something that a google employee may know.
Google update is something that comes like a wind. No one know when it will be and when it does come it takes everyone by storm. But these days there has been many small updates going on. Because few weeks back my dropped domains lost its PR. One PR5 domain tht i got from Namejet wen rocketing down to 0. So Google = unpredictable which i hate
I noticed that today some of my blog are gets the Pagerank changed... I think it was the minor update...because not all of my domain are changed..but I think it's such a great news for all of us..
Just had a quick look and nothing happening this end but it was odds on favourite that it would happen in the last week or 2 in March.
On average updates are quarterly. nobody knows for sure. remember it, write it down and don't start another PR thread! 1 star from me!!!