@httivals : Hi, where are you now ?
@Jono : Thanks
@Jorgen : You're basically right the K200D is better than an XTi or an E420 from a viewfinder magnification point of view. However httivals's approach is a top - down and a smaller viewfinder is a drawback.
To come back to httivals post, here some viewfinders's basic :
The higher the magnification, the bigger the apparent image size, the easier it is to focus. This is a bit les important in the digital age as we can put an autofocus target point where we want to have the focus. However, the manual focus correction is much faster and straightforward, for exemple for portraits. This value is normally given for a 50mm lens on a FF camera, so we need to take the crop factor into account.
A greater distance makes it easier to see the apparent image as a whole which is of prime importance for 'composing' a great image. This is also an important comfort point for people wearing googles or when you put sunglasses on your nose.
Here it is best to have a look through the viewfinder, high-end cameras have normally better focusing screen and are brighter. You may discover a lots of reference marks which are of no use for you and may be or not disturbing to you.
@Jorgen : Too many Pentax lenses suffer from high level of CA. By the way regarding Nikon you're not alone, I think jumping from my FE2 to a D90 by end of the year
@Jono : My table is only the theory, as you have some of the cameras listed in it, could you give an a comment on the differences between the viewfinders apparent image size of the E3 (@25mm), the M8 (@35mm ?) and the alpha900 (@50mm) ? I think, it may be of interest for some of us, thanks.