If you really want to know how much (academic) impact your work has, you can use publish or perish a free little program, that has been around for some time. The software uses google scholar to automatically retrieve publications you have authored and papers that cite you. From this it extracts several citation metrics, most importantly:
the number of citations per article and
the h-index, i.e. the number of papers (e.g. i) that have at least i citations each.
Once the program is installed it takes seconds to score oneself or one’s arch enemy.
Those of you not only interested in the own performance can use it to assess journals and quickly find most influential works in a particular domain of study.
Google scholar is arguably only the second best alternative to ISI web of science. But in addition to beeing free, the author of the program argues here, that it gives a more complete picture than ISI .
It is not open source and runs only on windows so there is some room for improvement.