Fluid Design

For as long as I've been designing websites, I've almost always designed using a fluid design- one that is set up so that it 'fits' the screen of the viewer, as often as possible. Obviously you can't fit everyone's screen, because some people use a small portion of their monitor to view the internet, saving another portion for their other open apps.
However, I feel this is the best way to go for most sites. If I use tables in the design, I set them so that they only use a percentage of the screen size. I did have a client who had purchased a template online, and we made some adjustments to it to customize for their site - he actually pulled out a ruler and showed me that the lines on each side of the design were not the same width, even though I had them set at the same pixel width. He also wanted the site to be perfect on his monitor, which was a fairly large one...
The problem with making a site 'perfect' on your monitor? You're forgetting that your customer is who you should be building your site for. My goal for website customers is to make a site that visitors can easily navigate, will enjoy viewing, looks good on their monitor, and is easily readable to them. That usually means, among other things, that I don't set exact font sizes in the design, but rather set it at 'large' or 'medium' according to how the font looks.
I do this for one simple reason - if I am on a site with tiny print, I will hold my CTRL button and use the scroll wheel on my mouse to enlarge it - if that doesn't work, I usually don't hang around very long. Life is too short to strain my eyes trying to read something in microscopic print.
Any site needs to look good, but it's most important that viewers can use it easily - and if they can't, what is that saying to them? "If you're not cool enough to use this site, then we don't want your business" is what it says to me. And I don't want to be responsible for a site that's saying that.