The Canon 5D purchased used is currently the best camera for the dollar by a huge margin. To surpass it in pure technical image quality you need to spend $8000 on a Nikon D3X or the newer 5DII

Sports shooters will want the Nikons or the 1DMIII for better place focus points but the actuall focus speed and tracking of the 5D is excellent when using L lenses in good light. In fact I have no issues regarding focus speed.

What is slow is the time it takes to view a raw image on the LCD. It takes what seems forever if you click more than once but just click once and you will be waiting about 5 seconds! This is the single biggest drawback.

Because there is a MarkII digital price rot has set in and this $2600 camera in October of 2008 is now selling on ebay for $1100 to $1400!

The 5d has nearly identical (slightly worse) 3200 ISO performance to the full frame and much newer nikon D3 and D700. At lower ISO's the 5D is clearly sharper. It is possible to get virtually noise free images when viewed smaller than 1600 pixels at 1200 ISO.

It can best be described like this;

Absolute perfection at 50 iso but you may get some purple spots in very dark shadows.

From 100 to 400 iso there is virtually no differnce providing the exposure is good.

From 500 1200 ISO it is difficult to tell the difference in most images provided the exposure is good.

From 1200 to 1600 you need to get the correct exposure for a clean image but it will be perfectly acceptible for even a 13*19 enlargment.

At 3200 a good image is a good image and the noise level does not get in the way. In fact at 3200 if viewed smaller than 1600 pixles (about 8 inches) noise is often not noticeble.

Another way to look at noise levels is if shot below 400 a noise free image is possible. Anything over that lacks the perfection but will appear perfect at 1600 pixel size if it was exposed correctly.