It seems that changing site-designs periodically isn't a rare phenomenon. I'm not really a designer, however I like to tweak ready-made designs for usability/functionality reasons. For example recently I went from a two-monitor 19" setup to a one-monitor 22" (wide) setup.
Comparing the two I arrived to the same conclusion I've heard from many sources before: two smaller monitors beat one larger monitor hands down. This is because on one larger monitor lines can become very long and hard to read (without head movement) and you loose the "grouping" feature of multiple monitors (the maximized windows occupy the entire monitor). To counter this I use the Desktops tool from
Where I was going with all this is that I added a max-width to my stylesheet. I've set it so that it only gets activated when the browser is more than ~1000px wide (in fact is it specified in EMs, so if you change your fontsize, the threshold will vary). I know that this is poorly supported in IE6, but that is only a very small segment of my visitors (around 10%). An other reason for me not implementing popular hacks for IE 6 (like CSS expressions) is that I wanted to specify the value in EMs, which is not impossible, but definitely tricky.