I have had a pair of Sennheiser HD600 for 15 years now as my main headphones. To say that I have got my moneys worth is an understatement. I use headphones a lot and have calculated that they have been on my head for around 2 or 3 years
The funny thing is taking account the inflation they have remained very similarily priced for the past 15 years, I think I paid 200e in 2002.
Expensive spare parts and fragile standard cable are my only complaint but its not that big issue anymore, you can get fairly good quality ear cushions from China and use the more durable HD650 cable.
I sometimes lust over the HD800s but the high initial cost and especially the "running cost" (meaning replacement ear cushions etc.) are kind of deal breakers for me.
I also have a pair of HD580s that I got cheap used as a spare set and numerous Porta Pros.