Importance:
AWA
AWA posts some stats that say Google reaches 80% of Internet users. (AWA later says that this came from a 12/03 Media Matrix report)
AdWordsAdvisor Says: [
Link to quote]
I am sort of in the camp of using both AdWords and Overture, and getting the maximum coverage. ;)
I'd say, though, that it's really important to truly learn each system in order to get the maximum performance out of it - and having done that, then adjust your spend for each to be in line with your conversions.
Now, if I had to pick just one, well, you already know the answer to that! :)
Actual reach figures? Well, this is not really my arena - but the recent 'Google reach' figures that come to mind for me are below. I'll try to confirm that these are current, and post again if I learn differently.
Reach of Google alone = approx 40% of Internet users.
Reach of Google + partner network = approx 80% of Internet users.
AWA
