Is it wise to use a Fluid Layout?

leaving 980 pixels unused in a 24" monitor just seems plain odd not to say wrong

I’d disagree here. If you’ve got a monitor with that high a resolution, you’re probably not running with a maximised browser window. And even if you are, are you really fussed that the content’s all in a fixed area in the middle? Really?

As long your site has a decent, useable layout, I don’t see the problem with space either side on high-res monitors.

I generally think that fluid layouts are a good idea. The problem starts when your fluid layout starts to get really wide with high resolution screens - there is a limit to how far the human eye can track horizontally without losing the vertical positioning. That is why newspaper columns, for example, are always rather narrow.

Try to look at wikipedia in a high resolution screen, and you'll see that they limit the maximum width to something around 800-900px - more then that (assuming a rather standard 12pt font) and people stop being able to read until the end of the line and then effortlessly find the start of the next line, and the whole thing breaks into a mess of eye and neck strain.

On web sites I build, I use max-width to limit the maximum width of the text content (and in that I also include images and other stuff) to about 720-800px, which with sidebars and such can possibly get to around 1000px. If the screen is wider then that, then either center the content of left align it (right align on RTL web sites) - both work well.

But you have to design your layout so that it flows when the available width is narrower - this is very useful for people with netbooks (which are rather popular now and I expect will become more popular in the future), smart phones and even small screen mobile devices. Such mobile devices more and more feature standard browsers and you should address this in your designs - even if a mobile browsers can reduce your website somehow, the "mobile mode" usually does this by messing up the page and killing your intended user-experience.