I have three D70 cameras - one is a D70S. It's a great camera as far as I'm concerned. My income is based on the quality of my images. Once you learn how to use it - as with any other camera - it can produce fantastic results. The D70S is the current model in production, and it focuses slightly faster than the first generation D70 it replaces and offers a larger LCD screen and remote socket. I've found the control layout to be intuitive and fast. It's simply different from Canon - as is Pentax, Olympus and Minolta/Konica. Once you get to know the menu, it's really quite simple.
8mp doesn't get you any significant increase in image quality over 6.5 mp unless you are intent on producing 20X30 or larger prints and you need to crop significantly.
The Canon 20D is a respectable camera, and it has fairly good high ISO performance, but somewhat inconsistent flash performance (well, by my standards, anyway). It's still a very good camera, but I chose the D70 for it's strengths. Those strengths are (a) reliability, (b) great flash metering capabilities for consistent flash exposure and (c) affordability vs. performance is excellent. The D70S kit lens (18-70mm AF-S) is also an excellent performer for the money.
In the past, I had the chance to switch to Canon. I didn't much have a preference either way. The D70 just felt better to me and I already had Nikon lenses anyway. Canon would have been fine, too.
As for a "shaky" shutter, what the previous poster is probably referring to is a bit of play in the mirror assembly. Shake a camera around, you'll hear it on some bodies. It has nothing to do with build quality. I can't hear anything when I shake my cameras and mine get banged around quite a bit. D70s are supposed to be rated for something like 25,000 exposures for shutter durability. I've got close to 70,000 exposures on one of my D70 bodies, 40,000 on the other. My D70S is new, so it only has somethig like 8,000 on it. I shoot anywhere from 1,000-3,000 images per week because it's my full time job.
If your budget is right around $1,200, the D70S is a great camera for the money to get started. The SB-800 flash unit is also perfectly matched to the camera.
If your budget is tight, you can buy a used mint condition D70 for around $550. Not a bad deal if you know where to look.
Good luck. Choose the camera that feels best to you. Play with them if you can. Don't listen to a sales person unless you trust them to give you an unbiased opinion. My local shop will push Canon one month, Nikon the next. They get promotional kickbacks from the manufacturers if they sell X number of units. That's why I order from NY.