I use these at the gym w a sony MD as a source. For comparison's sake, I have HD-600s and a Microzotl at home.
The isolation is incredible using the silcon flanged buds, but my left ear hurt quite a bit. The foamies are much more comfortable and the isolation is more than adequate. You sacrifice some bass in return for comfort. I listen to mostly acoustic and vocal music w/some older R&R. Think Lyle Lovett, Eva Cassady, Cowboy Junkies, Alison Kraus, Eric Clapton, Neil Young. The sound is really quite enjoyable. I make my own mixes using a CAL CL-10, and the 4X setting on the MDR. Its not going to win any awards, but its not fatiguing or unpleasant in any way. Clear, no distortion, nice mid-range and acceptable bass (better w/the flanged plugs but I have narrow ear canals so too painful. No microphonics at all w/the ER-6 cord and relatively easy to insert, even w/foamies. Highly recommended for walking around use. Using the silicon plugs, I WOULD NOT recommend them for mobile use as the isolation is very impressive and you could easily get hurt. Would be awesome on a plane, if not for the equalization issue. Anyone have any experience with the silcon plugs on a plane?