Since this seems to be a popular issue it deserves some extra chit chat.
Resolution is the number of pixels displayed. 1024x768 1600x1200 etc.
The great number of pixels the more workspace you have....sort of.....cuz it has to be useable.
Physical screen size is the corner to corner viewable size( 22', 21", ( really 21 and 20" ) etc and LCDs ( actual viewable 17") and has nothing to do with resolution....sort of.
Again it has to be useable - so a 12" monitor at 1600x1200 might be crisp but it cannot be read at a distance your eyes can deal with comfortably and that's another variable in all this.
It's not quite as cut and dried as I indicated in another post.
Physical screen size and the type of work come into play, video card and screen resolution as well and monitor quality and your visual acuity. A top end 19" might be more readable than a low end 21".
With the ability to dynamically resize text and docs and even the dock itself it gets hard to explain in an easy manner.
An example ( and others please jump in with illlustration of the issue ).
Being able to resize icons in X means you can get more icons into the same 1024x768 space - they get smaller - that's what your dock does as it has more fed to it.
On a 12" screen you would hit a point where the icons were too small to be useable FASTER than on a 14" screen despite the same pixel count being available.
Taking this to extreme I run a pair of 22" monitors one at 1600x1200 and one at 1792x1344.
Now that's a huge amount of pixels but sometimes at 100% imaging on a document, the text is too small - say our database with it's 9 point text. So I resize up to 150% for easy reading.
Safari makes this kind of resizing effortless and of course in graphics etc working at a variety of zoom levels is normal.
Again there are limits. My 19" monitor will also do 1792x1344 BUT I can't read on it what I can read on the 22" even tho the pixel count is the same.
When my eyes are tired I can either drop to 1600x1200 reducing the pixel count and "enlarging" each item on the screen but losing screen real estate or I can up my "zoom" level or font size document by document.
You have this choice on CRTs not on LCDs where the latter is the method.
Where your monitor is also comes into play. A 12" iBook by it's design pulls you into reading distance - the correct distance for all monitors while many run their large screens further away. ALL screens other than for presentation should be at reading distance as that's where your eyes are relaxed. Many put the monitor too far away, then up the size of the font or reduce resolution. This forces your eyes to "rest" beyond the reading depth = headaches.
You can test this for yourself by playing with various distances to the screen and varying the document/font size. If you "listen to your body" - you'll find a screen distance that most relaxes your eyes in focusing depth. This may be surprisingly close to you and often you will feel your eyes relax as your monitor comes in even an inch closer. ( you should also be sure to look away into the distance once in a while to give your eyes a chance to change the focal depth )
Take a page at 12 point Times or 9 point Geneva and 100% and play with the distance to the screen.
Likely you'll find closer is more comfortable unless you are in your middle age and resisting getting reading glasses
in which case arm's length will likely feel best.
In deciding on monitor size, dollars come into play as well. Obviously a 30" Cinema that multisynches perfectly is the dream monitor but reality dictates compromise and also we all have different eyesight.
I have 20/15 so what I find comfortable others find unreadable and vice versa.
Getting the best use of monitor size and resolution and quality ( ie buying a 22" to do 1024x768 is silly ) is a series of trade offs.
The OpenGl aspects of X offer a far greater degree of flexibility in designing your workspace onscreen to be visually comfortable yet efficient.
Many apps offer flexible resizing while others like some audio and video apps have a relatively fixed worksize offering little in the way of adaptable workspace forcing you to choose your monitor(s) very carefully.
ehMacs own text edit window is an example of this and Safari's easy resizing deals with it perfectly.
Exposé really helps Mac users as the thumbnail "flattened view" lets you perhaps use larger individual windows without losing the quick ability to navigate your way through 50 open windows and 20 open apps. ( keeping that one often used window peeking out in the corner eh [img]tongue.gif[/img] )
Figuring out the best use of resources for screen/dollar etc can be a real task. Sometimes 2x17" are better than single larger screen.
Whatever you do the screen is where you live and spending time and effort getting it right is worthwhile.