I don't think I'll get much argument on that here, but this shocked me when Saku-chan told me about it.
Even if my husband wasn't a scientist, I still pay enough attention to know that fruit flies are an incredibly important genetic model.
From Wikipedia (yeah, I know, but it was the quickest reference):
About 75% of known human disease genes have a recognizable match in the genetic code of fruit flies (Reiter et al (2001) Genome Research: 11(6):1114-25), and 50% of fly protein sequences have mammalian analogues. An online database called ****phila  is available to search for human disease gene ****logues in flies and vice versa. Drosophila is being used as a genetic model for several human diseases including the neurodegenerative disorders Parkinson's, Huntington's, spinocerebellar ataxia and Alzheimer's disease. The fly is also being used to study mechanisms underlying aging and oxidative stress, immunity, diabetes, and cancer, as well as drug abuse.