You may go above and beyond to get your job done, but stay away from using the word workaholic in a job interview. When you're asked about a workplace weakness, employers want to hear something more thoughtful than a contrived answer suggesting you will put their company at the top of your priorities. Even if you're truly a workaholic, but many employers would see it as a cop-out answer that doesn't indicate much about your ability to do the job.
Instead, try approaching the weakness question with a productive answer. The Wall Street Journal spoke with a New York psychologist who gave a great example of what I'm referring to: He recommended saying something like, "My weakness is I get bored by routine," as an example of how to respond when interviewing with a start-up. This technique can easily be applied to any position you're after.