Apparently u will go deaf quicker in ur ear if u use an enclosed headphone like the hd25's. Because they sit so well on your ear, a lot of pressure builds up in your ear. I use the hd25's and im a little more deaf in the left ear.
If i had to buy headphones again, i'd go for something open. Check out the headphones Dave Clarke's using at the moment. They're Sennheiser's but i've never seen em in shops tho. They sit flat on your ear if that makes sense. Just a thought.....