Great question this one, does the Google search engine change?

If so, how often?

How does this affect my site rankings and overall online strategy?

Recently reported by Amit @ Google, that in 2010 there were at least 2 changes per day.  That is for the year of 2010 there will be over 730 changes to the way Google produces search results.

This is very important, for having a website that is constantly updated content wise and having a resource to assess quarterly your strategic online direction can mean the difference between ranking one week and falling off the radar the week after.

Stay up to date, work "on" your business, not "in" your business all the time.  MAKE time to understand how your strategic online direction can benefit your business.