My thoughts on the PSB M4U compared to my Polk UltraFocus 8000.
Initially I found that the PSB's made me feel like the music was in the back ground, and a bit flat compared to the Polk's but over time this has changed and the music seems to be slightly more accurate that the Polks. But there is not much in it. The only BIG difference is the noise isolation, when I had the Polk's cranked up the whole office could hear my music loud and clear, they didn't mind and the comments were that the music sounded amazing! If the PSB's were still $599NZ I would not have purchased them, but at $299NZ they was too tempting.
Over all the PSB's sound more accurate but the Polk's sound a little richer. Maybe after some time this may change as the PSB's are only an hour old, and the first pair was only 5 days old.
I have had some trouble with the PSB however.
Both pairs have some cracking where the cups swivel, is this normal, and a crack above where the 4 and U are on the left cup where the rubbery plastic is. This was on both sets. Both sets of batteries died very quickly and the first iPhone cable was a dud.