In-ear versions work great, but they aren't for everyone. I like them and use them for some applications, though I don't have a custom-fitted set. I fear the possibility of blowing my head clean off if I make a mistake with these in. I prefer my Sennheiser open-ear version for recording, though. The Sony is an industry standard for home studio recording and I have a pair, but I prefer the open ear to a closed ear as I think it is less likely to fatigue and cause damage with heavier use. For lack of a better term, I believe the open ear versions are more forgiving.
Active noise canceling versions are great for air travel, but I would never record with them. Effectively, they are distorting the signal, in a positive way to cancel the noise, for comfortable listening in a loud environment. We have a set of Bose and I find that they are a bit scary as they create positive pressure within the ear cups that bothers some people, the Mrs. foremost among them.
Use for listening is different from use for recording/mastering, though. For recording purposes, you have to understand the properties of your headphones or monitors with regard to coloration of the sound. Paul's lesson above, about listening and switching headphones, is critical if you want to come out with mixes that sound good on a variety of systems. I always listen to my stuff both on a set of studio monitors and through the headphones before pressing the button to mix down.
-bob
