It depends on how much of the data gets thrown away in compression.
A standard 60-minute mini-DV tape holds the equivalent of about 15GB of data.
This is about the same as a DAT DDS-3 computer backup tape which is mechanically very similar (but quite deliberately not the same
) and which holds 12GB of UNcompressed data and perhaps a few GB more if compression can be used.
There are camcorders that use MPEG compression to pack the data more densely and then one can store an hour's recording in a few GB. Whether the loss of quality is noticeable is a matter of opinion.
The main drawback of a cam with a hard disk in it is that the data cannot be taken out - short of transferring to a PC. This is stating the obvious I know, but (as someone who has done their share of "home movies"; one's kids mostly) I can tell you that you must not believe the hype about the whole world being into creating home movies! It just doesn't happen. Transferring a video to a PC and editing it (using the software provided), adding in music, etc, is fun to do once or twice and after that one gets thoroughly fed up with it.
But one still wants to preserve the precious footage of one's kids growing up. Where to store this? One could transfer it to a 400GB PC hard disk; OK until the HD crashes and then you lose the lot. One could back it up to something, but what? It's a LOT of gigabytes. I really don't see many people buying a £300 DDS3 or DDS4 tape drive and backing it to computer tape!!
So, the smartest thing is to just keep the original DV tapes. They have quite high coercivity (i.e. once magnetised, they are hard to erase) and will last for at least 10 and probably 20 years. One day, soon, when we have optical disks that hold 1000GB you will transfer the whole lot to one of these. Until then there is no better way to store the stuff than just keep the original tapes.
That's why I think all camcorders that record onto anything but DV tape are a waste of time - except for special applications where the recording is always immediately processed and the original can be dumped.