I've had these headphones since time immemorial. I have the HD540 Reference, the ones whose ear cups have a velvet rim. They are the most comfortable headphones I have ever worn. The cups' protective cushions wore out pretty quickly and I had to replace the cable once, but they still work fine.
They sound precise, very nice and quite natural, not too flattering, especially in the lows. I have even managed to mix a couple of things with them without any unpleasant surprises.
I really hope they last for a long time, because I'm very satisfied with them.