A few people have been discussing this topic of late and it's worth a mention in the context of what to expect vis-a-vis US economic growth in the coming months.
The observation is that as market confidence in a US economic recovery has become stronger, stock markets have shot upwards but bond yields have not. One would normally expect bond yields to also go up as money moves from bonds to stocks during economic recoveries. This "anomaly" is interesting and worth watching.
Tyler Durden at Zero Hedge (1/30/12): "Yields Plunge Most In 3 Months As Equity-Debt Divergence Remains"
Joe Weisenthal at Business Insider (2/7/12): "PRESENTING: The Great Market Disconnect Seen All Around The Globe"
Joe Weisenthal at Business Insider (2/18/12): "This
Is STILL The Most Glaring Anomaly In The Market"
Tyler Durden at Zero Hedge (2/20/12): "As Everything Disconnects And Everything Is Soaring, Morgan Stanley Issues A Warning"
[Also worth a look - this Aug 2011 post by Felix Salmon at Reuters: "Chart of the day: The great earnings-yield divergence"]
It's also noteworthy that stock market trading volumes have been noticeably lower in recent times - and it's happening at a time where revenue and earnings growth has also declined (outside of Apple) and upside guidance from companies is also on the decline.
P.S. Joe Weisenthal has an observation from Doug Kass that there is also a marked divergence between the S&P 500 vs. the ratio of Dow Transports to the S&P 500. Transports, I would presume are at least in part affected by rising oil prices at a time when overall world oil consumption has been on the decline. Additionally, the potential impact of QE and liquidity type actions on stock markets and commodities like oil can't be emphasized enough.