Dear friends
I seek your advice on my situation as I am really confused, I landed on Sept 2006 stayed one month, left Canada to settle some issues, returned to Canada on may 2007, I had to leave again on December 2007, my question is how much time is left for me to stay outside Canada to maintain my PR????

I think you have to be in Canada for two years in a five year period.

Which I think means back by March 2010 and then don't leave again until August 2011 at which point you would have had PR for 5 years and been in Canada for 2 of those 5 years. You would probably want to come back earlier to give yourself some room in case you need to leave for an emergency without losing PR status.
As an aside the rules for Citizenship are different and you need to have been in Canada 3 of the last 4 years (last time I checked) so that would require actually living in Canada.