i have experience of 15 days with Widgetbucks so i can tell you how to earn a lot with widgetbucks:
1) use ads type 160x600 (best paying for me) because in big size banners more products showing than small size banners you can check this by own.
2) use the electronic products ->> cell phones ->> my 95% of earnings are from these ads and other ads dont paying a lot because peoples attract toward cell phone more than anything. (i experiment this).
3) create new widget for every new page you are going to add WB ads because accroding to me WB will not approve clicks from unknown page thats why while creating new widget they ask that where you are going to put his widgetbucks ad.
i already earns 213$ in 9 days and my earnings with adsense is very low compare to this (just 130$/month or less than it with adsense)

see this pic, most of my earnings come from cellular accessories and cellular phones and 90% of my earnings already approved
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rep+1 for this great and first ever trick to boost your earnings with WB.