I'm considering getting a used Nikon D300, D700, D3 or Canon 5D Mk11 if I don't get a D200 that is and was wondering how good these cameras are if left in Auto Focus mode or Fully Auto mode or however fully auto works on these cameras. Currently I don't know how to use any of these cameras to anywhere near their capabilities, but will learn. I know that to buy a camera of the calibre of the ones I've listed is missing the point of them to use them fully automatically or is it? I guess what I'm trying to ask is if they will give better pictures than cheaper cameras in auto mode or do they only come into their own when their features are fully utilised manually? Thanks in advance for any replies I may receive.
Leaving aside the 'politics' of your purchase for a moment, here are a few things that you should be aware of concerning the Nikon D700 (the only one that I own on your list

).
First off, it does
not have a full "Auto" mode, nor any "Scene" modes - unlike all of the entry level DSLRs. The closest that you can get to "Auto" is probably "P" (Program) mode, which will choose both the shutter speed and the lens aperture for you. It won't necessarily change other setting like ISO and flash activation, which some DSLRs
will do when used in scene modes. In short, it's not really designed for being used in this p&s way :shrug:.
That said, with the absolute minimum of effort (a morning's reading of the instructions and playing with some very basic settings), anyone would be able to get to grips with using "P" mode and the vast majority of people would have no trouble at all in understanding which speeds in "S" mode will give them the levels of movement blur (or rather, lack of camera shake

) that they need to get good pictures. From there onwards, it's just a small step appreciate the benefits of choosing the aperture size yourself and any curious and intelligent person (as your post implies that you are

) would soon be happy shooting in "A" (Aperture) mode too, I believe.
Where more advanced cameras like the top Nikons really come into their own for capturing great images in the hands of a total beginner (IMO/IME), is with their fantastic 51 point auto-focus feature and their great control of metering and white balance functions.
This anwers the first part of your question; yes, the D700
will perform the auto-focus 'better' than a much cheaper DSLR, IMO. If you leave it set to auto area focus, it can recognise all kinds of different scenes (including people's faces, landscape features etc.) and will usually pick exactly the right areas to focus on. What's more, if you want to focus on a specific point in the viewfinder, you can switch to select any one of the 51 AF points and move a little red around the viewfinder (using the direction arrow buttons on the camera back) until it covers the area that you want to be your main subject and focus on it. With a 3 point AF system, you can't do this nearly as well - if your subject isn't directly under one of those three points, you have to move the camera around until it is and then recompose the image, whilst holding down the AF button (or shutter release).
Even after several months of owning both a D40 and a D700, I still occasionally screw up otherwise great pictures on my D40, by not selecting the correct AF point (out of the measley three available :razz

, whereas the D700 rarely lets me down on this front.
Now for the poilitics

!
You sound a bit like me, 7 months ago

. I started with an entry level Olympus DSLR and immediately began to find limitations with it wanted to change it for something with more "growth potential". Against the advice of about 65% of people here, I went straight for the Nikon D700 and just ... learnt to use it :shrug:! Even though I'm only an amateur togger and haven't managed to get the best out of this great camera yet, I can already appreciate some of it's finer qualities (great low light shooting image quality with high ISO settings, big clear viewfinder, ergonmics and ruggedness etc.). I've never regretted my decision to buy this camera for a moment and doubt that I will want to upgrade from it for a very long time - if at all!
I say, if you can find the money - do it! If after a month it's sitting on a shelf because it turned out to be more hassle than you thought, stick it back on eBay and you'll get 95% of your money back

. I'd bet that you
don't though

!
Good luck!