Can't speak for anyone else (no-one's ever worn mine for more than a few seconds!) but mine fit like a glove. I've had them on since 9am this morning, and it's now 5pm - pretty much non-stop. They're not tight or uncomfortable, although I do occasionally have to move them slightly just to let the skin around my ears get some air (but hey, that's going to be an issue with any headphone of this type).
They're also fine for walking around and travelling with, which I do quite a lot of. Again, not too heavy and not too tight.
I haven't tried to wear them while undertaking any exercise, but I'm not sure I'd want to risk dropping and potentially damaging them while out running or at the gym!
They are actually better for exercise than most headphones on the market- the clamp is just right and they are light enough that they don't slip.
Maybe my head size is smaller than the average person. I have the headband adjusted to 0 and I've tried twisting the headband to make a tighter clamping force. For normal use it's fine, but when I try to do pushups or jogging, the headband tends to slip off my head. :x