This is an interesting post that I'm often coming up with the 'dilemma' of what's best - and there is no 'right or wrong' in this situation as it depends on the site, the management, the amount of information provided on the site, the depth of the site, the amount of images, the purpose of the site and the intended audience.
It's easy to get stuck into one type of design method - in fact it's probably the 'safe' way when doing generic sites where the majority of them may fall into the 'fixed width' site by very nature of the information they provide, but the fact that we have alot more reading on the screen, I find it increasingly annoying to scroll. However, having visited a developer company and seeing the guys coding on their 22" wide screen Dell's, it was handy - but at times - a little more difficult in reading all the way across - but these guys seemed to be used to working in this space, and often used the 'wider screens' in they way I use my own '3 monitor' setup.
I guess that's why I had the page resizer XFLEX written and now with a new developer involved, have some more plans for it's development in the future. It brings about the comment of 'you cannot please everyone' but at least XFLEX brought about some compromise, but what it's done, I feel is made it harder to develop a site to a certain extent because in the design process, you need to compensate for the fact it will be viewed in different ways. (although there are settings that can be overridden to allow % or px management) This means you could have a site that really needs to be controlled a bit more offer resizing through having 800px, 1024px, 1600px or whatever ... through to 800px, 1024px or 100% - and the layout will change without page refreshing. It also allows for text resizing which I'm seeing more sites using these days.
But management of information is harder.. you need to look at having a different approach to 'fluid and flexible' layouts in my opinion, and that does restrict you in your design, since sticking to 800 x 600 is really very easy to work with but not a good use of space in my opinion on sites that have alot of depth to them. But it's just my opinion and when I read stats on monitors, browsers used to visit my sites within my network, 800 x 600 is really 'old hat' these days, but still should be considered when creating brochures type sites I suppose or doing 'generic one size fits some' appraoch.
I noticed our newsite in AU http://ninemsn.com.au - has gone to 1024 width and for good reason - they would have done their research.
The outcome is.. easy on the eyes, less scrolling, and probalby for them - more room for ads, but my point is.. they have updated to the wider screens in response to the type of audience they have, however, we do also have some news sites that are 100% width and it's great reading from them! Also again, only my opinion, reading online is completely different to reading offline, printed matter. The whole process in how we transfer information and absorb it.
So there is no real 'right or wrong' in doing either full or fixed width websites, but what could be perceived as 'wrong' is not taking in time to consider the all aspects of the site before making the final decision.. and of course - the perfect way would be to give your viewers a choice and install xflex on there 
. But then the onus is back to you to be able to design something that works on multiple screen options.
Ths topic will always be one that instigates opinions, and by nature makes it one where no one will disagree. Having said that - I do create 800 x 600 sites still but think it's really limiting based on the expectations of the viewer these days.
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