How long do your jumpers last?

[clutterfly]

My jumpers from last winter are all looking really tired. Perhaps I should have hand washed them.... Or maybe they're only meant to last a year...
Can anyone shed light on their jumper health please?! Am I destined to buy new jumpers every autumn?

I keep them a few years and then wonder why I feel scruffy...just seems so wrong to have to ditch them after a year, but with the best will in the world they bobble or matt up. I wash at 30 on a wool cycle in the machine with delicate liquid. My boobs seem to make them go out of shape too!