Since long I was using the mail server provided by my hosting company. Then I heard about hosted services from Google (http://google.com/a).
My mail server was having some problems & I wanted to try hosted services, so I moved my mail service to google.com
Before moving to google, the spam count on my mail server was ZERO (I mean it) & now I can see atleast 5-6 SPAMs daily in my mailbox. I agree that SPAM detection of google is very nice but why SPAM started in the first place, my account was very clean before this.