My faithful readers know I believe in circumventing HR whenever possible in the job search process. That philosophy is based on the fact that HR is not intimately familiar with the needs of different departments and the fact that most HR folks are not skilled in either interviewing or hiring.
A new article addressing questionable practices by HR by Nick Corcodilos is well worth the long read. http://www.asktheheadhunter.com/newsletter/OE20050823.htm#continue.
If you have to go through HR to get the job, at least you will be a little better prepared. If you can possibly target the decision-maker directly, it is always a better choice.