Recent Cochrane review published on financial incentives and quality of healthcare in primary care  shows that the jury is still out. "there is insufficient evidence to support or not support the use of financial incentives to improve the quality of primary health care. Implementation should proceed with caution and incentive schemes should be more carefully designed before implementation."
In the last couple of years some research published by Imperial College in London suggested there was some benefit for certain types of patients in diabetes.  
Quality interventions are often multi-factorial. Although they may appear to have high face-validity but to be certain that particular aspects work as intended more careful study is required of how they change behaviour. The jury is still out on whether 'pay for performance' is beneficial.
1. Scott A, Sivey P, Ait Ouakrim D, Willenberg L, Naccarella L, Furler J, Young D. The effect of financial incentives on the quality of health care provided by primary care physicians. Cochrane Database Syst Rev 2011;9:CD008451. Available from: http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD008451.pub2/full
2. Alshamsan R, Millett C, Majeed A, Khunti K. Has pay for performance improved the management of diabetes in the United Kingdom? Prim Care Diabetes 2010 Jul;4(2):73-78. Available from: http://www.ncbi.nlm.nih.gov/pubmed/20363200
3. Millett C, Bottle A, Ng A, Curcin V, Molokhia M, Saxena S, Majeed A. Pay for perfomance and the quality of diabetes management in individuals with and without co-morbid medical conditions. J R Soc Med 2009 Sep;102(9):369-377. Available from: http://www.ncbi.nlm.nih.gov/pubmed/19734534