I love my ER6i's, but...
1) Using them is a commitment. It takes me 15-20 seconds per ear to put them in and 5-10 to take them out.
So if I'm going to be in an environment where I need to hear anything, or people are going to be talking to me from time to time, I think twice before using them.
Zune, Wii or iPhone?
Virtualization: Running Any OS Within OS X
ER 6i from Etymotic Research - I can't hear you! No, really, I can't hear you!!