While the RAE may make some marginal fields more acceptable, as Mary
says, it also can negatively affect other areas, such as heterodox
economics.  If you want to know of the impact of the RAE on economics
and heterodox economics in particular (not to mention the history of
economics), you should look at:

Lee, F. S. 2007.  "The Research Assessment Exercise, the State and the
Dominance of Mainstream Economics in British Universities."  Cambridge
Journal of Economics 31.2 (March):  309 - 325.

And if you want to examine the data associated with the article go to
http://cas.umkc.edu/econ/economics/faculty/lee/docs/rae-app.pdf.

Two additional articles on the impact of the RAE are the following:

Harley, S. and Lee, F. S.  1997.  "Research Selectivity, Managerialism,
and the Academic Labor Process:  the future of nonmainstream economics
in UK universities."  Human Relations 50.11:  1427 - 1460.

Lee, F. S. and Harley, S.  1998.  "Peer Review, the Research Assessment
Exercise, and the Demise of Non-Mainstream Economics."  Capital and
Class, 66 (Autumn):  23 - 51.

It should also be noted that it is not just the ranking of journals and
the RAE that has a negative impact on the history of economics (and
heterodox economics) in the UK.  It is also the state sponsored
benchmark for economics which almost (but not entirely) writes the
history of economics out of what is to be taught to students and
completely excludes heterodox economics.  This is direct professional
qua state control of the content of an academic discipline--control
which UK mainstream economists seem quite happy with.

Fred Lee