erm, didn't mean to be so brief.
Adsense a nice little cash cow (for me; maybe a lot more for others) and I'd imagine clicks in stock market/financial can be worth quite a lot if well-targeted. I put it on an inactive site at a whim and forgot about it and just discovered last week that it's been making me money off this practically dead site.
I'm now putting it on all my non-adult pages.