Hi Anon -
Like many other plants (specially when grown in cooler climes) the perennial aubergine (egg-plant) is actually a perennial that's treated as an annual by vegetable growers, especially here in the UK. As are others like the runner bean, the tomato, potatoes etc. etc.
From a botanical point of view it's easy to see why British gardeners distrusted this plant when it was first brought to our shores. Aubergine (Solanum melongena) is a tender perennial of the nightshade family (Solanoceae) which, as well including potatoes, peppers and tomatoes, also includes some very poisonous plants.
The plant itself is a herbaceous perennial, and as I said above grown as an annual in cooler climates such as the UK, and it has a habit that is broadly similar to that of the pepper, albeit with larger, fleshier leaves. Despite recent advances in breeding cultivars suited to our climate, aubergines are not particularly cold tolerant and tend to under-perform if grown outside.
If you live in a warmer climate over there on the other side of the pond then it'll love being outside - as long as it's kept well watered (it's NOT a desert plant!)
Hope that helps -
G.
http://gardenerschat-shed.net/
http://aeronvale-allotments.org.uk
