AdSense is turning eight tomorrow (See the official announcement here). I never realized until yesterday that I was using Adsense almost 13 months after it launched i.e. from July 15th 2004!
You can see in my post about What Makes Me More Money And How Much? that Adsense still makes me 1/3rd of my total income online.
Check out some of my articles on Adsense to get you going …