Pros: Very comfortable, seems durable, sounds very good
I think the best way I can describe myself is an aspiring audiophile. I haven't the money, or the time to audition high end gear. That being said, I do scour the internet for information and save up my pennies for things I really want, and that's where the B&W P5s come in. I was able to experiment with them several times in an Apple store before finally exchanging two previous pairs of headphones I had bought there; one being the Skullcandy Aviators (which sounded surprisingly good despite their track record) and the other being the Klipsch Image One headphones. While purchasing these at their 150 dollar price points, I still knew I was making a mistake in not saving up and just pulling the trigger on the P5s. Luckily I was within Apple's 14 day return policy and in possession of a shiny new paycheck.
The P5s originally caught my eye at the store because of their beautiful, classy, sophisticated look. As I walked over and picked them up, I was astounded by the craftsmanship that went into designing these. Sheepskin leather ear pads, and otherwise metal construction. Seems fitting that it would be in an Apple store. In any case, they are very lightweight, but solid feeling at the same time. Picking it up, you can tell you have a quality product in your hands. I am almost afraid to bring them out into the real world. The only gripe I could possibly bring up would be the somewhat thin cable that it uses. However, this possible shortcoming is allayed by the fact that the cord is replaceable and cleverly accessible. The ear pads are magnetic, and removing the left side pad reveals that the cable is connected not at the base, but snakes up towards the top. I like this because it takes away stress that would normally be subjected to the plug and directs it more towards the main part of the cord.
I have not had the luxury of trying out really high end, full size cans, so I can only compare them to what I've used before. I have a pair of Shure SRH440s (among a few others) which I've always thought sounded really good; excellent balance and whatnot, but the ear pads are almost hard and make lengthy listening session difficult. It also has quite a long, thick cable, making it a hard choice for portable headphones, even though I know they're not really meant to be. In any case, the P5s are the best sounding headphones I've heard to date. The bass is...delicious. It's not overpowering, but you can feel it, and more importantly, distinguish it. The mids are nice and powerful; very in your face, and the highs are sparkly and clear. I listen to primarily classic rock, and these deliver in a big, comfortable way. Also, if you're listening to low bit-rate files, the P5s will grab you by the shirt collar and let you know immediately.
Once again, being an amateur in the world of headphones and high quality sound, this would really have to be my first real foray down this road. I have read that there are better sounding headphones for the price, but with this kind of care and design in build quality, craftsmanship, and comfort, the B&W P5s stand out from the crowd, IMO. If you can find the money, I definitely recommend these to anyone looking for a better listening experience.