Recently, in information science, perhaps due to the proliferation of easy to use biblio-tools, there is a renewed interest in understanding and measuring the impact of research publications and authors.
I learned from Dannyfest and Don Norman that there is a new tool appropriately called Publish or Perish. It is available for free-download for both Windows and Linux. Alternatively, you might use the web version of a different tool instead called QuadSearch. Publish or Perish calculates a bunch of citation impact analysis metrics, and one of them is a metric called h-index, which has gotten considerable interest lately in information science.
It is also sometimes referred to as the Hirsch Index or Hirsch number.
A scientist has index h if h of his/her Np papers have at least h citations each, and the other (Np-h) papers have no more than h citations each. So, as an example, I used the tool to calculate my h-index, and found that I have a h-index of about 19, which means that I have 19 papers that have at least 19 citations, and I have no other papers with more than 19 citations.
For comparison, Stu and Danny have h-indexes in the high 30s (39 and 36 respectively). Johan, Peter, Jock Mackinlay have in the low 30s (33, 31, 30 respectively). Victoria Bellotti, Mark Stefik are around low 20s (24, 23 respectively). You may be interested in downloading the tool and trying it out to "measure" yourself and your friends. :) Maybe it will inspire you to do greater and more impactful research! Or maybe it will just boost or deflate your ego! Use with caution!
Hirsch suggests that, for physicists, a value for h of about 10-12 might be a useful guideline for tenure decisions at major research universities. A value of about 18 could mean a full professorship, 15–20 could mean a fellowship in the American Physical Society, and 45 or higher could mean membership in the United States National Academy of Sciences. Clearly, the numbers needs to be adjusted for computer science related fields, due to the different nature of our publications (more conference papers, etc.)
PS: BTW, you should take care in choosing the fields on the left hand side, so you avoid picking up bad citations. This is one of the best tools I have seen (even better than the SCI [Science Citation Impact] one, because it appears to be more comprehensive.)