Yes, if your site draws a high volume of traffic in a good niche. We have 4 million visits a year (over 6 million page views) to our website, which is law related - a good niche. AdSense generates substantial revenue from that, more than what most people would consider a full-time income. We also get revenue from other sources. We tried affiliate marketing but it didn't work for us. Might work better in other niches.