I am currently an ABC student. I think its worth the money if your just starting out. Some of the material seems pretty basic to me but I feel I have learned a lot too.
If you're already a trainer and have established a business I think Cynology College might be a better choice (and more affordable), if your just looking to enhance your knowledge, because the course work is more in depth (I'm a student here too). Many of the courses are approved as CEUs for the CCPDT and IAABC.
Attending seminars is another way to go. Even if you can't attend you can purchase many of the seminars on DVD from tawzerdogvideos.com . I haven't gone to any seminars yet but I do have several on DVD and they are well worth the cost.
Raising Canine
home offers live or taped telecourses that I have also heard great things about.