Are Workaholics Mentally Ill?

I'd say yes.  Jordan Weismann looks at studies of workaholics:

Even as the precise outlines of workaholism remain a bit fuzzy, various studies have tried to identify its physical and emotional effects. At the risk of carrying on like a Pfizer ad: research has associated it with sleep problems, weight gain, high blood pressure, anxiety, and depression [3]. That’s to say nothing of its toll on family members. Perhaps unsurprisingly, spouses of workaholics tend to report unhappiness with their marriages [4]. Having a workaholic parent is hardly better. A study of college undergraduates found that children of workaholics scored 72 percent higher on measures of depression than children of alcoholics. They also exhibited more-severe levels of “parentification”—a term family therapists use for sons and daughters who, as the paper put it, “are parents to their own parents and sacrifice their own needs … to accommodate and care for the emotional needs and pursuits of parents or another family member” [5].
How many people are true workaholics? One recent estimate suggests that about 10 percent of U.S. adults might qualify [6]; the proportion is as high as 23 percent among lawyers, doctors, and psychologists [7]. Still more people may be inclined to call themselves workaholics, whether or not they actually are: in 1998, 27 percent of Canadians told the country’s General Social Survey that they were workaholics, including 38 percent of those with incomes over $80,000 [8]. (Even among those with no income, 22 percent called themselves workaholics! Presumably some were busy homemakers and students.)

I'm definitely not going to claim to be a workaholic.  Personally, I think I'm generally only good for about 5 or 6 hours of solid office-type work a day, with 8 or 9 hours on a really good (or crazily busy) day and 2 or 3 on a really bad one. It would be nice if I could structure my days as George Soros suggests, only working the days or hours when you are really going to get something done.  Now my sister, on the other hand....