Sand - 3:25 am on Jun 11, 2013 (gmt 0)
I have a site that's about 2 years old. It gets tens of thousands of daily visits from Google, and usually less than 100 a day from Bing. I actually get more traffic from Ask.com.
Bing has hated the site from the day it was born. Looking back through my analytics, there was never a spike or a dip. It's just been predictably miserable since day 1 (this was a new domain at the time, never registered before).
I've never had this problem before with any site. Usually, Bing has been the easy one.
I realize this is a very hard question to answer, but have you seen anything in the past that impeded ranking well on Bing?