I am considering taking the exam to become certified in HR Management.  Is this necessary if I have years in the field?  Does it benefit me a lot?  Is the test hard or does it have a high pass rate?  Do I need the expensive study materials needed?  Who can give me some insight on this?

From experience (both as a seeker and poster of jobs), I see that a PHR/SPHR/GPHR is having an increasing importance in the field. Many businesses now have that a PHR is a plus or even required for higher paying/responsibility jobs.

 I like to think of it like driving a stick shift car. You can only go so fast before you have to downshift and go faster. You can only go so far in the HR World with a 2 year or 4 year degree before you need to "downshift". This downshift can include a PHR Certification or even an MBA. Once you complete the downshift, you can now go faster than before. Long story short, the benefits depend on your particular goals. Being Director of HR or Vice-President of HR for Microsoft would certainly include a PHR or SPHR in the future. However, this now applies to being an HR Manager or even HR Generalist in some businesses.

The PHR and SPHR are nice to haves, but definitely not must haves.  I know when I've interviewed in the past most employers don't understand what PHR and SPHR actually are.  Some consider them simply pieces of paper saying you were smart enough for a couple of hours to guess correctly.  Others think it's on par with having a CPA.  While the tests are easy, they're definitely not the same as getting a CPA! 

I have my SPHR.  Has it helped me?  Maybe.  But I don't think it has helped me enough for me to have ever worried about getting it.  Having a Masters would help me exponentially more. 

 I think the pass rate for PHRs is now running around 65-68%.  For SPHR around 55-60%.  It's a hard test, but if you are a good test taker it won't be all that difficult.  I didn't use any study materials and didn't do a whole lot of preparation.  I joined an on-line study group but rarely paid attention to the e-mails that came through.  The only area I didn't feel 100% confident in was unions (and the SPHR seemed to have quite a few questions on union environments) even though I have worked with unions in the past.  I didn't have a lot of direct involvement.  So I spent some time reading various things on line about unions, union negotiations, labor relations, etc.  I had almost 20 yrs HR exp with a lot of it at the upper management level (strategic).  Passed on my first try. 

 HRCI has some practice tests, I did those and found them helpful.