When someone uses "search the web" option in my site's Adsense for search, does he gets to see all Google search ads or only ads that target the content network ?
Have you read the FAQ for Adsense for Search yet? If not, it might help explain it better for you. This is a link to the question "How is AdSense for search different from Google Free search?" https://www.google.com/support/adsense/bin/answer.py?answer=9882&topic=144
I guess that answers the question... Should have assumed so... seeing as Google has made it clear (design wise) that the adsense search SERP's are not to be confused with the regular old friendly google SERP's... therefore people who opt out of having their adwords shown on the conten network won't wont their ads shown on content network generated search results.