According to Seth Godin, on his blog, workaholic people lives on fear. Workaholic people are not happy doing their job, they simply go to the office because they think they had to. To qoute:
It was hard to imagine someone being passionate about mining coal or scrubbing dishes. But the new face of work, at least for some people, opens up the possibility that work is the thing (much of the time) that you'd most like to do. Designing jobs like that is obviously smart. Finding one is brilliant.
The person is just compelled to do the work. Seth Godin has mentioned the other worker who is the passionate worker. By the word itself you would know what kind of worker he or she is.
Although, there are a lot of times that people associated the word workaholic in a more positive way, there are still chances of getting misunderstood. The negative side of the word is that it was coined in an era where we see -"aholic" as addictive which is negative.
I personally believe that in anything I do, I have to put my heart on it for it is an honest conduct not just for someone else to notice my conduct but being true to myself. I am the one doing it so I must be, at least, honest to the last person who will understand and respect me and that person is me, myself and I. I say, doing something out of fun is more likely to be a passionate worker than doing something for a compulsive need to work, that is a workaholic.