I really don't send many emails through Gmail, but when I do it is INSANELY accurate in its suggested sentence completion. Sometimes simple stuff like an address or whatever, but it can get really creepy when I'm sending something to my wife as a reference for some bill or interaction with our landlord and it knows exactly what I'm trying to say after just a word or two (sometimes, something like "Hey, I just..." and it has the rest of the sentence ready to go).