That sounds like a weird mixture of truths and falsehoods to me.
Nobody can send you any emails (spam or otherwise) unless they know (or can guess at) your email address. Web browsing doesn't divulge your email address to anyone (irrespective of the data collection that is carried out by firms like Google), so it's impossible for Google (or anyone else) to send you spam based upon your web browsing habits.
Google does offer a free service to marketers, called Google Analytics, which collects certain data (but it still can't generate spam because, again, it doesn't collect email addresses):
http://en.wikipedia.org/wiki/Google_Analytics
If you've got a GMail account, Google will scan all of your mail, specifically so that it can append appropriate advertising material. Some people object to this:
http://www.privacyrights.org/ar/GmailLetter.ht m
However that has nothing to do with web browsing.
Chris