Well my player arrived earlier this week so I've got to do a review on it soon.
The thing is tiny. It is by far the smallest device out of all my audio players. It weighs a lot less than my Ipod Touch, which is bonus as that thing always felt too heavy for rear jean pockets.
Audio quality out of the box was simply outstanding on Super.Fi 5 Pro's. I had to tinker with the JetEffects audio settings to use my HD595's and HD515's because they just had bass overload otherwise. I haven't had the chance to really use it that much though as I've been getting lifts home lately instead of me using the bus
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Imo the audio quality is almost equal to iRiver's quality, but much more open in regards to the tweaks you can do.
Having been spoilt by the untouchable ease of use OS/UI sitting on the Touch, its hard to feel at home with anything else. The D2's interface obviously isn't as good, nor is the touch screen. Unlike the Touch's screen, which relies on the static on your fingertips, the D2's screen is a tactile touch one so it isn't as sensitive nor accurate if you see what I mean. The interface could do with more work in places, but its otherwise functional.
Transfer speeds to the internal memory are nothing to write home about. Using the USB cable on Vista x64 I get around 4-6mb per second, and around the same speeds when writing to the 8GB SDHC card - so as James mentioned, it's best to use a card reader when writing to the card.
Battery life, well I've been using it on and off for about a week now and have yet to see it drop down a bar - out of four.
This player is primarily for music and radio use. It is superb for the former, whilst average on the latter. The picture viewer is pretty rubbish in this day and age though, the screen size nor resolution just isn't large enough. The funky paintbrush Notepad app is rather neat though, but doesn't work too well with the touch screen sometimes.