My current project is a pair of RRDS 31/36. I use them at work for about 4-5 days a week and wear them hard in all kind of weather. They're about 2 months old now and my plan is to keep them going until may 2008 before the first wash.
RRDS 10 months old - washed 5 times. First wash in 60°C after 8 months (worn 4-5 days a week), other 4 washes in 15°C with a small amount of Woolite . Same jeans unwashed after 7 months of wear: