Well, I just got my D3, and suffice to say, my experiences have been mixed. Firstly, yeah, it's slow right after bootup. I have an Android phone, and it has that same lag right after you turn it on. My guess is that Android does all that "house-keeping" stuff, like syncing, checking for updates etc during startup and it bogs the device down. For my D3, I just switch it on and don't touch it for a few minutes - until it settles down
Having said that, the UI is still a bit laggy. There is a noticeable delay between pressing the on-screen buttons and the response. The same thing also when pressing the 3 buttons on the bottom of the player (the Return, Settings & the Home key). Sometimes it takes multiple presses before I get a response. I can only hope that it's software related, not hardware. Android is notoriously unforgiving on wimpy hardware (CPU and ram).
I updated to the latest firmware X.31 firmware (mine was 4.31 btw). Software stability is still not quite there, yet. Skipping to the next song sometimes causes stuttering in music playback. Heck, for no particular reason that I can discern, in normal shuffle play some songs do stutter in the beginning before settling down. It's like what happens in the older HD based players when you accidentally bump or knock the player. Fortunately, it doesn't happen all that often, but it's still often enough to bug me. On the other hand, it does seem "shuffle" play REALLY does work, at least I've been hearing different or "new" songs that I've never heard of in my S9 & J3. Heh, my D2, S9 & even the J3 all have a propensity to play back the same series of songs, "shuffle" play notwithstanding. The D3 doesn't seem to have this "bug" during my music listening.
And yeah, I've learnt to keep a safety pin handy. The player has froze on me several times...when playing music, and several times when playing video. And it didn't just freeze...the player got really, and I do mean really hot while in the frozen state. The screen goes black, and all buttons are un-responsive. Only the safety pin in the reset hole worked. That's just not cool (pardon the pun
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Charging the player is also finicky. Apparently, only the supplied charger can reliably charge the player. It can only charge from USB only when it's in "sleep mode". If you plug it into your PC's USB port and play with your phone, it doesn't charge. Now I have plenty of devices, and it is the first time I come across this "feature". Heck, even my Android phone charges when connected via USB and I'm mucking around with it.
The reason I try to overlook all these is that the SQ is really, really, good. In fact, I can pretty say with confidence that it probably has the best SQ among all the players I have. As a point of comparison, the S9 & the J3 sound pretty much the same. I certainly couldn't tell them apart blind-folded. The D3 is audibly superior, to my ears. The highs are crisper, and the bass is tight and goes deep. There is a spaciousness in the music that is only apparent if you listen to the J3 and then quickly switch to the D3 with the same music. The J3 sounds "mushy" in comparison. I use a JH13 as my earphones btw, and it's quite revealing on any change in your audio chain.
All in all, the D3 does show promise. The awesome SQ does go some way to compensate for its numerous flaws, but I do hope that Cowon will keep pumping out those firmware updates to polish it further. And yeah, regarding those firmware updates...please resist the temptation to add anymore apps until you fix the stability of the D3!
**Appendum**
Oh yeah, forgot to mention the USB transfer speed was slow. Man, filling up my 16GB was an excercise in patience. The J3 was a speed demon compared to the D3.