A few days ago I wondered how spammers had found my newly created Gmail account. I received some interesting feedback. Perry E. Metzger writes (this and the other message quoted with permission):

If you ran email systems, like I do, you would know that they are inundated constantly with guessing attacks. One would try blocking these, but they're always launched from zombie machines and any given zombie rarely does more than a trivial number of iterations...

Charlie McMackin:

I noticed this a while back when I started getting spam at the exact times I was browsing Myspace. If I had been to gmail once during my browser session or if gmail was open in another tab, I would get spam. Upon a quick look at the cookie info, if one has the gmail -chat feature enabled, you can see your email in pristine plain text form ready for harvesting.

Of course I'm not absolutely positive, I just thought the correlation of getting spam only while I was using gmail or had used it once to be quite suspicous.