I'd also like to add some more comparisons.
The HFG30 is $1700+taxes which is a very hefty price compared to other similar models minus some of the extra features the Canon has that can be had for nearly $700 less.
The Sony PJ790 has 96GB of internal memory whereas the Canon HFG30 has no internal memory.
Internal memory is useful in that you can't and won't ever forget or misplace your SD cards. You can also use it to store files and movies and such.
The HF30 with its dual slots does allow for relay recording (meaning if your slot 1 card is full, it can start recording onto slot 2 card seamlessly). It also allows for you to record in both AVCHD and MP4 simultaneously if you needed to do that (wherease the PJ790 does not allow simultaneous recording).
The HFG30 also allows recording of MP4 files at a higher 35Mbps bit rate vs the 28Mbps bit rate of the Sony.
The Sony comes with Night Shot mode which is always an intriguing and useful option if you ever record in very low light or darkness but don't want to use the camera light. It's that very cool looking military green tone where you can see people in darkness.
The HFG30 has 5 assignable custom buttons. This is very useful in that you can assign some frequently used functions to these buttons so that you can access them in 1 touch. It's often cumbersome to have to go back into menu settings, browse through all the folders to change/adjust settings. So these assignable buttons are very convenient. The Sony does not have any assignable buttons but it does have a quick access function on the front jog dial (but not as convenient still as the assignable buttons on the canon).
Also, the canon has a jog dial for the viewfinder. This means when looking through the viewfinder only, the Canon allows you to go into menu settings using the jog dial. The Sony doesn't have a jog dial. So if you are using the viewfinder only, you can only zoom in and out. If you wanted to adjust settings, you would have to pop open the flip out screen again and use the touchscreen to browse through the menu.
The Sony IMAGE STABILIZATION is hands down the best in this market. The SteadyShot technology (swivelling lens) makes for smooth recordings even when walking or moving around. Give the PJ790 the edge in IS over the HFG30.
HFG30 has faster autofocus. There are 3 options in the Canon's that allows for instant AF, fast, and medium. The PJ790 at times can take awhile to find it's focusing right (when in autofocus mode). I find that manual focus is better and quicker, but sometimes I need to rely on the AF when I don't have the time to do it manually .
The projector screen does have it's uses. While it is a luxury that isn't necessary, it can be very useful when you want to present something without a computer/TV present. Simply use a wall or any flat surface and you want watch /view pictures and videos for all to see. Great for sleepovers and nighttimes when you just aim at the ceiling while in bed and enjoy the memories with your friends.
The PJ790 also turns on and off automatically by simply opening and closing the flip out screen or viewfinder. It's rather convenient because you don't have to press a button to turn on or off the device. It also has a manual power button on the inside of the fold out screen. Some might prefer that the device doesn't turn on and off when you flip open or close the screen as in the HFG30. You need to manually press a power button on HFG30 to turn it on or off. Depends on your liking. I personally prefer the auto power on with open flip out screen. It's very convenient and quick.
The HFG30 is larger and heavier. Not that the PJ790 is a small camcorder itself. It's also pretty heavy, but if size matters to you, then just be aware the HFG30 is a larger camcorder. Not your typical camcorder size. But both are incredibly solid and sturdy builds. They feel strong and solid.
The HFG30 is a couple hundred dollars more than the PJ790 and offers a little more options. If money isn't an issue for you, then the HFG30 is for you. If you're looking more for something less expensive yet still offers competitive quality and options, then the Sony PJ790 (or even better, the PJ760 which is identical to the PJ790 except for the mic and the brighter projector light, but will save you $500 compared to the HFG30), then the Sony is for you.