So, it appears Bing is rolling out a new rewards program as mentioned in the Bing thread here in S.P.A.M. SB doesn't currently offer AA miles as a reward so it seems Bing gets the point there, but it seems that you can earn SB faster than Bing rewards. For example,
this article says Bing users can receive 8 credits a day maximum for searching (which would require at least 40 searches a day), and a $5 Amazon gift card costs 541 credits. So basically, if you max'ed out on searches every day for 68 days, you'd have enough for a $5 Amazon gift card. I don't know if SB has a maximum but I would say that with regular searching (and hardly ever entering in special codes from the blog, etc), I'm earning a $5 Amazon gift card about once a month. I'd love to jump ship from SB to something better, but aside from better rewards (such as miles), I don't see Bing Rewards as being it.
If I'm missing something, I'd love to hear about it.