Same here, not much irritates more more than a web page that is like 600 pixels wide running down the middle of my wide-screen monitor.  Then they try to fit 2-3 columns of information in that tiny space!  I tend to zoom in on the page to try and simulate a wider page and then spend my time scrolling up and down.  When only a couple of words fit on each line, it's like reading a teleprompter!

But, people that write pages without using tables are forced into making them a fixed width (so they can get the table effect, without tables), so expect more of them to start showing up online.  Maybe I'll start running multiple browsers side-by-side!

Then again, I've entertained the idea myself of making my own sites fixed-width to avoid the problems discussed above, but so far have resisted the temptation.   A good website design can flow out onto a wider monitor and still look good, it is just very difficult to do right.  When displayed on monitors that are over 2K pixels wide, dynamically flowing websites look significantly different (ever stretched a page across a four-monitor system?).