Spambot postings on the web are such a plague, that it seems impossible now to offer a form without some sort of "prove you're human" protection. For fellow asp.net fans, here's a free and easy CAPTCHA control to integrate: http://recaptcha.net/plugins/aspnet/.
And if you're new to this, and not quite sure what CAPTCHA is: it's one of those warped images of letters and/or numbers that you may be required to discern and type into a webform before submitting it.
The term "CAPTCHA" (think "capture") was coined in 2000 by Luis von Ahn, Manuel Blum, Nicholas J. Hopper (all of Carnegie Mellon University), and John Langford (then of IBM). It is a contrived acronym for "Completely Automated Public Turing test to tell Computers and Humans Apart." Carnegie Mellon failed in its bid to copyright the term.
Wikipedia's article on Captcha describes it as a reverse Turing test: a machine administering a test to a human, rather than the other way around. More about Turing tests, for the endlessly curious, at the online Stanford Encylcopedia of Philosophy http://plato.stanford.edu/entries/turing-test/.