I received mine today (Batch 2), listening to it at the moment. My previous DAP was a Cowon V5, an A3 before that, and a Sansa Clip+ for ultra-portable, IEMs are Westone 2s. I was a bit worried about losing the BBE suite from Cowon but was pleasantly surprised with just how well the DX50 sounds without any adjustments - better than the Cowon with FX, and far better than any of them 'naked'. So far I've just been running some 24bit FLACs and I'm loving the clarity and soundstage, though I did notice some oddness in the soundfield on some of the Civil Wars / Barton's Hollow tracks if I wasn't dealing with earphones I would have put it down to phase issues.
Build quality is great, as someone else mentioned it is sturdy yet lighter than you would think, the physical buttons have a very solid feel also.
There were some earlier comments on the screen protector, I did receive one with the unit (inside the main packaging).
Customs wise - no charge, it was marked as a USB soundcard.
Anyway, I bumped up the bass a little as the 2s are not great naturally in that dept. and am loving it so far, well worth the money.