Pros: Clean low end, fun to listen to, detailed sound, high quality, light.
Cons: Clamping, bad with glasses.
I love my HD25-1 II Headphones. They are, in my opinion the perfect portable headphone. I am not a huge fan of on-ear headphones but I do quite enjoy them. The sound quality is addicting, they are easily driven by an iPod or iPhone and have quite a bit of low end (perfect for modern electronic music), but when put on a proper amp the low end levels out the headphone becomes much more accurate.
The only real problem I see with them is they have quite a clamping force and when put on with glasses can become very uncomfortable. I use them for a max of 2 hours.