Like it or not the academic world is slowly (or perhaps not that slowly) moving towards being judged by how highly cited our work is. Actually, it is not a bad measure as if you publish something and nobody ever reads it, or refers to it (i.e. cites it in their own work), then was their any point in publishing that research?
The problem is, of course, that it might takes years (perhaps decades; or even more) for somebody else to recognise the value in a particular piece of research. The other problem is that once scientists know that they are being evaluated in this way, they find ways to maximise their citations (they are typically quite clever people!).
The next research assessment that will be carried out in the UK (called the Research Excellence Framework (REF)) will using citations as a major way to measure the impact of the research that is carried out by individuals, research groups and universities.
If you are interested in the REF take a look at http://www.hefce.ac.uk/Research/ref
At the moment, in the UK, this area is the subject of heated debate in the scientific community and this will be the case for the foreseeable future, especially when you bear in mind that the last research assessment (Research Assessment Exercise (RAE)) has only just been completed (the results were announced in December 2008 – http://www.rae.ac.uk).