It sort of makes sense to me that Google, in exchange for giving me a free email account, would email ads to my free email account. Microsoft always has; I can't tell you how many times I saw "Hotmail (1)" on my MSN screen and clicked through only to find it was some ad for some Microsoft thing or another. At least with Google's version, it's very, very clear that these are ads; they don't even make your inbox get a (1) next to it or anything.