Yes, it's definitely a great improvement over the D30, in many ways.
In no particular order:
1. The strap eyelet on the right has a smoother and wider curve, making it easier to thread in the strap. A very minor detail, but makes a difference.
2. Exposure is more accurate. The D30 was constantly underexposing, and needed EV +1/2 or +1/3 most of the time. The 10D is spot on. One thing to note is that the LCD default brightness setting (3) is a bit too bright, and may make your picture seem overexposed (but this is not the case, if you check the histogram). I initially dialled in EV -1/3 until I realised it. Reducing the LCD brightness to level (2) makes the LCD preview more accurate (but always check the histogram anyway).
3. I've already mentioned the much better AF. Today I let the camera choose which AF point to use, and it's accurate 85-90% of the time. So I just frame the shot, without worrying about which AF point is being activated, and having to recompose after achieving AF. A true P&S camera. But I would probably still choose the central AF point and recompose for critical shots.
4. E-TTL was reportedly (on depreview) more accurate, so I bought a 420EX and tested this. Bingo! No more wildly varying exposures, depending on where the AF point was. No need to FEL then recompose. Just set your exposure settings manually to whatever you want, and fire away. Perfect exposure every time. Those with long memories will recall I had sold off my 420EX in disgust due to its performance with the D30.
5. You can now set the external flash to emit AF assist but not fire. This is a bit moot, now that I have an ST-E2 as well, but it was an option not available on the D30. I understand the D60 had this option?
Oh yes, the image review IS definitely slower, but that's OK with me. The other complaint on dpreview was about the dial on the back being flimsy - I find that it's not so, just that it's not ribbed. In fact I like the feel of the new dial and set button better. Smoother.