- mid and late 2007 MBP update
- early and late 2008 MBP update
- early and mid 2009 MBP update
- 2010 was the only time there was just 1 update (recently)
- early 2011 MBP updated - seems quite likely there will be a late 2011 MBP update in the September - October time period.
Perhaps research before posting.
Then there is the Mac Buyer's Guide on this very site:
MacBook Pro - Neutral - Mid-product cycle