I was making around $100 per day until my account was unfairly banned last year. I did get re-instated after my appeal but they kept two months of my earnings so now I only use Adsense to fill 10%-15% of my ad space and only use it on low traffic sites. I'm still making about $30-$40 per day but I'll never trust adsense as long as they have their banning publishers without warning or without explaination in place. In all honesty, getting banned by Adsense is generally a lucky strike for most publishers because it forces you to think outside of the box for monetization (which is how I found TNX, my best moneymaker)
Make sure you experiment with different positioning and formats with your adSense. As a member stated, just changing the layout increased his earnings $3.00 per day ($100 bucks a month can pay a bill or two). Utilize the channels to track different performance stats so that you can A/B test. For those of you that can do a bit of programming, code your page to display one set on odd numbered days and one set on even numbers... this way you can view the monthly report and take away valuable information. Colors / Layouts / positioning / page content / directory names / proper html / seo compliance... all of these come into play for targeting adsense. I'm here to help... let me know if you want me to look at your site and suggest improvements.