It's all part of the quantitative easing, right? I can't imagine shorting bonds at the moment unless it's a long-term trade. Betting against government manipulation seems quite risky.
"One trader cited by Bloomberg noted that companies are eager, even desperate, to show they hold only ultra-safe T-bills on their balance sheets for fourth quarter earnings reports so they're willing to accept the negative or zero yields" http://www.guardian.co.uk/business/feedarticle/8135756