A couple of months back I made the mistake of importing all of our Adwords campaigns into Bing overwriting the "bing only" account we had setup.
Immediately I seen our conversion cost become anywhere from 2-10x the cost of Adwords per AdGroup.
After some investigating I figured out this huge jump was from broad match modified words. I'm aware of the dangers of broad match and the keywords I have on this modifier on Adwords remain profitable. However, with Bing it is almost a joke on how indiscriminate they are.
For example, for the last 7 days consider the performance for identical keywords:
Bing Impressions: 1,794
Google Impressions: 167
Bing Impressions: 909
Google Impressions: 16
Obviously apples to apples, there's no way Bing can send 10-100x more traffic from its search engines.
My conclusion is that Broadmatch modifier is of very little use with Bing and one must be very careful when importing Google Adwords campaigns.