The main reason i have mine is for the food - veg from supermarkets is appaling compared to what you can grow yourself. Why is it Tesco's economy carrots smell of cresote when you boil them?
Also, my dad and both my Grandad's had allotments or big veg gardens aswell, i always liked helping out at weekends, school holidays etc.. I used dig my grandads veg plot for pocket money i was that keen! Of course the interest wore off for a few years later after discovering Beer, Girls, Cars and illeagle raves etc.. but i really apreciate having one now - especially when people post stories of long waiting lists etc..