My understanding is that it's meant for situations where the marriage has been relatively long, and one spouse has essentially given up his or her earning power to stay home to raise the family. I do think that's actually reasonable. I know someone, for example, who is in her 50's, and was married for roughly 25 years. Most of those 25 years were spent at home, raising their 3 sons and dealing with the household. Her husband decided to have an affair, and then to divorce her. She was awarded alimony for (I think) 7 years) and has gone back to school to provide herself with a career. I think that's fair.
I know another woman with 4 children (12, 5 yo twins, 3). She also stayed homw to raise the kids, etc. Her husband walked out when the youngest was 2 weeks old. She was also awarded alimony for a period of time. I think that's fair, too.
What I can't abide is spouses (because men do alse get alimony at times) who feel it's their *right*. The last thing I wanted from my ex was alimony - yeah, he should help support the kids, but I'd be damned if I would take a penny from him for myself.
Hope that helps!