My thoughts.
I was able to finally give my new D10 a listen to this weekend, and I must say I'm extremely impressed. So much so, that now I don't think I can carry my iPod + Westone 3's without the D10 anymore.
Before I go on, I must confess that I'm a noob to this whole thing, but have finally 'seen the light'. It's an expensive hobby yes, but has completely renewed my interest in personal listening. That being said, I don't really know much about the differences between different amplifiers or earphones, and I'm really only going on whatever I read here. I'm glad this resource is here simply so I know which product to buy in different price ranges.
When I first opened the box, I was surprised at how small the D10 is. This is my first headphone amp, so I was a little worried about the size after seeing comparison pictures. However, in reality its no bigger than my iPod or iPhone.
Operation is easy, which is good for someone like me without experience in amps.
The sound is awesome. Seriously. I'm still waiting for the iPhone/iPod copper LOD cable that I got off eBay (which was in my budget), so I'm only listening to this thing with the 3.5MM Male to Male cable that came with D10, using either my iPhone 3G's or 160 GB iPod Classic's headphone out. The difference between the D10 and the headphone out's of the Apple products is night and day. I'm hearing little things I've never heard before in the regular music I listen to, and my music is only either 160 - 320 kbps MP3's, .AAC's, .m4a's, or .m4p's. Nothing spectacular by any means, but I don't consider myself an audiophile.

And yes, the one bad thing about it is, it does have the GSM/GPRS/EDGE radio frequency interference issue that other's have mentioned - and I've only used it on the NYC subway. I hope the interference isn't terrible walking around outside.
In conclusion, I'd say any people lurking here from the Earbudes/IEM forum, possibly looking to improve their listening experience with their nice, new high-end earphones should definitely looking into purchasing an amp, especially something so easy to use and immediately gratifying as the D10. I'm pretty happy with the sound I'm getting, and I've really only had this thing 'burning-in' for a total of like 6 hours. I want to eventually try rolling the amps, especially if it could improve the sound further. I believe the D10 through the Westone 3's is a great combo.