The HG10 is significantly smaller than the HV20, though at 1 pound, 4 ounces, it's not a whole lot lighter. And though it weighs a tad less than its main competitor, the Sony Handycam HDR-SR7, it's also a bit taller; the silver-and-dark gray body doesn't look quite as snazzy as the SR7's mostly-black chassis, though. The taller body does, however, make it easier and more comfortable to grip.
To squeeze the body, Canon moved and reshaped a lot of the controls. In some cases, as with the large, extremely smooth and comfortable zoom rocker switch and the extendable eye-level viewfinder, the changes work for the better. Some things, such as the nontethered accessory-shoe cover--you might as well toss it now, it's bound to get lost eventually--should have been changed but weren't. And others simply disappointed me. Take, for instance, the new four-way-plus-Set switch with the concentric scroll wheel. On one hand, it's far better than a touch screen. But it's very hard to use the directional switch without moving the scroll wheel, which ultimately makes navigation and manual focus difficult. (Canon also dropped the manual focus dial from the lens barrel.)
Furthermore, the joystick on the HV20 is also better located. It sits on the body of the camcorder rather than the LCD bezel. So with the HG10, you're forced to shoot using the LCD far more than necessary; that's not just annoying and harder to hold steady, but you end up wasting a lot of battery power.
For the money, though, the HG10 delivers a pretty well-rounded set of features. The 3-megapixel CMOS chip shoots native 1,920x1,080 HD video, which then gets downconverted and interlaced to 1,440x1,080 AVCHD. It can also shoot 1,440x1,080/24p, although support for this flavor of the format is even more limited than that of vanilla AVCHD). Its 40GB hard drive stores between 5.5 hours of video at 15Mbps to as much as 15 hours of video at 5Mbps. As usual, however, I don't recommend dropping below the highest quality level, unless you're absolutely certain you will never want to edit the footage. You can snap 3-megapixel stills in photo mode or take 1,920x1,080 grabs while shooting in movie mode. But I find it utterly ridiculous that stills can't be captured to the hard drive, only to a MiniSD card.
The Set button on the LCD bezel calls up shooting controls for backlight, exposure compensation, focus, and quick review; in camera mode you also get flash controls. In video mode, a membrane Function button accesses the choice of program, shutter-priority, aperture-priority, Cine mode (for a film look, to go with 24fps shooting), and slow-shutter Night mode; a handful of white-balance options; various image effects presets, plus customizable color depth (for a posterized look), sharpness, contrast and brightness; a few digital effects; video quality; and still grab size. For still photos, you can also select from evaluative, center-weighted average, and spot-metering modes; continuous-shooting and bracketing; and photo size.