First of all, good question. Very good question. You should turn this into a hub.
I want to break it down this way: Work ethic is healthy. Workaholic (notice the "aholic" suffix) for me conjures emotions of addiction and negative behavior. It's more of an obsession with no limitations.
With all that said, work ethic sounds and should be a positive stand where we all build a sense of accomplishment, productivity and high self esteem. While being a workaholic can lead to chronic stress, behavioral issues and perhaps isolation from family, friends and nature; which can be detrimental to the human spirit.
Therefore, honestly, draw the line by first assessing yourself and stepping away from what may be potentially dangerous to your physical, emotional and spiritual well being and what is going on around you and with other relationships.
In the grand scheme of things, having a strong work ethic should not lead to a negative outcome. You have to learn to find that thing I'm always striving for--balance.