From my DSM based textbook and class notes combined:

Bulimia nervosa must meet the DSM criteria of

*repeated binge eating (there is no specific criteria for this, but perhaps 2,000 calories in a space of two hours eaten by a petite person might be a good start for visualization)
*repeated purging to prevent weight gain
*symptoms at least twice a week for at least 3 months
*self-evaluation highly dependant on body shape and weight

...and is differentiated from anorexia nervosa by body weight (see below). The difference lies in the body weight and not the purging; some anorexics purge (again, see below) Also, bulimics tend to have fluctuating body weights. There are two types, the purging type, and the nonpurging type, in which the compensatory behaviors are fasting or excessive exercise. Bulimia is often comorbid with depression, personality disorders, substance abuse, and conduct disorder.

90 percent of known bulimics are women, and there is a 1-2% lifetime prevalence of it in women. (Lifetime prevalence refers to the amount of people who will develop the disorder at some point in their life.) About 70 percent of bulimics recover, but 10% stay fully symptomatic.
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Anorexia nervosa must meet the DSM criteria of

*refusal to maintain normal body weight (85% or less of normal/minimum body weight)
*although very underweight, extreme fear of being fat
*loss of menstrual period

There are two basic types, restricting types, in which weight loss is achieved by restricting food intake, and binge-eating-purging type, in which the subject also regularly engages in bingeing and purging. It is linked to depression and is frequently comorbid with depression, some anxiety disorders, and some personality disorders. Men with anorexia are also likely to have a mood disorder, scizophrenia, or substance dependence.

A little less than one percent of all women develop anorexia; it is ten times less likely to develop in males. 70 percent of patients with anorexia eventually recover, but it is not nearly as frequent for the person to recover after the first treatment.
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Eating disorders are in general most common in industrialized nations. Media influences eating disorder prevalence a great deal; five years before Fiji had access to television and mass media, for example, there were virtually no eating disorders. Once mass media entered the scene, eating disorders became apparent with statistical significance (I do not know the exact numbers.)

Other risk factors include:

*Being female
*Adolescent/young age
*A higher socioeconomic status
*Troubled family life

Additionally, Caucasian females are more likely to develop eating disorders than African American females, however, this has started to even out recently.

Risk factors for men include:

*Athletic involvement (especially cross-country runners)
*Higher body weight in adolescence
*Homosexuality

Hope this is helpful!