"I don't like spending time capturing high definition video from tapes I record with my Canon HV20, but I also don't like the video quality I get from hard disk camcorders. Can I bypass the tapes in my Canon HV20 and record direct to my hard drive?"
Any camcorder with a FireWire connection can be used to capture directly to a PC hard drive, as long as you have software that supports capture. As you point out, this is a great way to save a step and avoid capturing video from tape after you record. In some cases, this is also a good way to reduce noise your recorded audio, because you won't get bleed over from the tape mechanism.
Some of the commercial video editing apps, like Sony Vegas and Pinnacle Studio, offer support for this type of capture, others require you to do the capture using some other tool. If you primarily use Roxio Easy Media Creator or Windows Movie Maker to edit your videos, you'll want to follow the steps here for capturing and editing your video. As a side note, if you are currently using a hard disk camcorder, this particular capture method will not work.
For capturing video direct to your hard drive and bypassing tape you need to install two things. The capture application we will use is HDVSplit. To capture audio from your camcorder, you also need to install a version of FFDShow. Once both of these are installed, you can proceed with capturing.
Capture HD Camcorder Footage Direct to Tape
The first thing you need to do is connect the DV port on your camcorder to the FireWire connection on your computer. Turn the camera on in Camera mode, not Playback mode.
Launch HDVSplit and configure a few settings before you begin. Because you're doing a continuous capture, you should probably uncheck the Scene split box, because otherwise the software will chop your video into smaller chunks. Choose a file name. Select a folder where you want your captured video to be stored. You can open a preview pane by checking the Preview box, which is good for confidence monitoring before you start recording, but in general, I recommend relying on the camcorder's viewfinder. After all the initial configuration is done, simply click the record button and HDVSplit will happily record video to your hard drive until you click the stop button or until space runs out on your hard drive.

Once the footage is captured to your hard drive, you can edit it in most video editing applications. As noted above, this method works with Roxio Easy Media Creator and Windows Movie Maker, neither of which supports live capture. You can also use freeware app Avidemux to edit video after you've captured it to your hard drive.
If you use Sony Vegas or Pinnacle Studio to edit video, simply use the built in Capture utility in those programs to go direct from camera to hard disk.