Well, I'm still burning them in diligently. I believe I'm up to about the 35 hour mark, which is where some have said they felt burn in time was enough for the HD280's. I'm going to take them up to the 100 hr mark, for completeness sake though. So far, I've noticed an increase in bass response since first getting them. To me, certain tracks have a good amount of bass, and plenty of extension so far. I kind of like the balanced sound that these cans give... no real emphasis in one part of the spectrum compared to another. It can take a little getting used to if you are a basshead or are used to cans with a little more bass punch, but I feel like the HD280's will work for me. As it stands, I do not feel like they lack in the bass department as others have commented. But then again, I have not heard the DT770's. I feel that they will work especially well for the role that I am assigning them -- as monitoring headphones.
Oh, and they isolate pretty well -- but they do not completely wipe out everything (especially lower tones). Compared to when I tried the MDR-V6's, the HD280's definitely give more isolation. The comparison factor for me on this was that I cannot hear people talking to me from 5 ft. away with the Senn HD280's but I could with the MDR-V6. One of the reasons I opted to try out the HD280's was because I was hoping to use them on the airplane to cut out some of that low rumble... but I think I am going to have to get some ety's to do that more effectively.
In the comfort department, the headband could be a little uncomfortable. It is very flat, and kind of pushed down on top of my head. My girlfriend commented that she felt like it was clamping her head (so it's not just a looks thing... they feel kind of vice-like too). But I foresee them getting more comfortable as I use them more (as in, the cans will probably stretch and flex a bit with time).