Here's my experience as an actual owner of the JVC MG555 Everio series HDD digital camcorder.
I love it. I love everything about it... except the process of getting onto the computer. The individual who said it is "harder to edit" may be misleading you; I find it much easier to work with HDD cams because it's so easy to record, organize, transfer, and store data; one great feature is that you don't have to wait for the whole length of the video to transfer it. For example, with miniDV, if the video is 45 minutes long, it will take 45 minutes to transfer it from camera to your computer. And, you have to set the tape by rewinding it and starting from the correct position. I don't even like dealing with tapes honestly, so the HDD is perfect for me (plus there's no tape motor recorded into the video).
With the MG555, it records to a .MOD file. This is actually a .MPEG file in disguise. Pull it off the camera in back-up mode (you see the HDD like it's a regular connected drive). One catch: there's no audio unless you convert it. There are numerous programs that can do that for you, one is MPEG Streamclip. It's freeware, and it converts to a variety of formats. You can change all sorts of things, too, including the quality, size, interlacing options, audio, etc. You can convert to the Quicktime format (.mov), .AVI, .DV, or as a MPEG4. You can possibly convert to other formats, but it may require plugins or codecs.
I am using MPEG Streamclip cause it's free with no nag-screens. FFMpegx also works, but that is technically shareware (even though you can use it as long as you want).
Once you have the MOD on your computer, without even changing the extension, you can open it up in MPEG Streamclip and convert it however you want. I then import it into iMovie HD (6.0.3) or into Final Cut Pro (5.1.4). Both programs are able to use it just fine, and there's no noticeable loss of quality for what I can tell. Granted, I'm not a professional video editor, but I am somewhat picky about quality and I hate pixilation.
Some will complain about the time it takes. Unless you're doing a bunch of conversions, it's actually faster to pull the file off the MG555's HDD, then convert it. That's compared to running a miniDV tape along with recording it to the computer at the same time. And that's really what you do with miniDV tapes; you "record" them into your computer more so than "transfer." It's unavoidable, of course, because it's a tape.
One more thing. Using my version of iMovie HD, I can record the HDD's movies onto my computer just as if it were a miniDV tape using the built-in import function. I haven't tried iMovie 8 (heard lots of bad things about iMovie 8 in general). I cannot yet get Final Cut Pro to import directly from the MG555 (but I haven't tried much, since it's so much easier for me to just download it from the HDD and convert).
I love my MG555. I had a miniDV Canon camera (ZR series); hated it to the core, everything about it. And much of that hatred was for the whole miniDV tape issue.