I've been in HR for approx 12 years, but I have primarily been on the HRD side vs the HRM side. The HRD side is focused more on the learning, organizational development, change management, etc responsibilities. The HRM side is more focused on your common HR management or administrative responsibilities as previously mentioned in this thread, such as benefits, HRIS administration, employee relations, etc.
From a general perspective, I have enjoyed my career and the productive work I have been able to do. I find satisfaction in contributing to development initiatives that actually bring value to the individuals within an organization and contribute to the overall productivity of the organization. That being said, I'll give you some of my personal general warnings about HR/HRD.
First, when things are going good, organizations are willing to invest in developmental efforts, but when there is a downturn, often one of the first areas on the chopping block is the training function. I personally have accepted this as a consequence of doing something I enjoy, but there is a reason that a number of experienced learning/org development professionals on LinkedIn have been employed across a variety of organizations and industries. Just be aware of this if you go this route.
Second, prepare yourself in the event that you are surrounded by unmotivated or indifferent people. There are definitely exceptions to this, and I've been on a few teams where we strongly worked together for a common goal, but in some organizations there are individuals who have been shoved into training/HR roles simply because they have no other useful place within the company. Someone in some position decided that such an individual could do minimal damage in the HR department, so thats where they were dropped.
Third, if you go the HRD route you will probably be involved in a number of pet projects or "feel good" initiatives in which you question the value or productivity that they bring to the organization. My personal perspective is that anything a L&D or HR organization does should add some strategic or tactical value to the organization. However, because of the limited ability of many L&D organizations to demonstrate their value to the bottom line a number of them engage in a laundry list or shotgun approach to justify their worth to the organization. They get it done (or sometimes don't), then head off in search of another fire or feel good initiative.
As far as education, I am currently in the HRD program at A&M. while I am enjoying learning concepts that compliment my experience, I do believe there is a significant difference since the HRD program is under the College of Education and the HRM is under Mays. I'll finish sometime next year, but I'm already considering getting another degree that will be more focused on the HRM side so that I can diversify my skill set a bit. I've been talking with Cornell about their online Executive Masters program, and it looks very interesting - but I'm not sure if it would apply to you since that particular program looks for individuals with a good amount of experience in the field. However, they also have a Master of Industrial & Labor Relations program available. I was unaware of the University of Illinois program until this thread, but I'll research that now.
Sorry for the essay, but just trying to help. One of my regrets is not getting enough info earlier into my career, so I try to pass along whatever I know and help anyway I can.