Gartner released some research last week, summarized in this Computerworld article ("Gartner: Five reasons why offshore deals go bust"). I think they are charitable in a number of ways, but the five main reasons they identify are:
Unrealized cost savings. As they point out, while offshore salaries may be lower, the additional costs of management, travel and infrastructure can rapidly eat into those savings, and for shorter-term projects (they suggest those less than one year, for certain) these costs may actually exceed the labor savings. For a more elaborate discussion of this issue, see my comments in late '04 "Thinking About Offshoring As a Solution: What's The Unit of Measure?"