I especially find the targeted gmail ads useful. I normally ignore ads as a habit, but the links put in the "Web Clip" section are usually quite relevant.
Every time I notice a relevant ad in my Gmail, it reminds me that I really need to find a way to protect the privacy of my email.
I've never understood why people feel that way. You don't mind a computer scanning your emails to detect spam, why do people mind when it is scanned to select unobtrusive advertising? Maybe I'm just desensitized, which is a scary thought.