Having seen thousands of websites, I always pondered why new companies are still designing in tables. On their website they state that they know the latest technologies, are efficient with code and compliant...etc. Yet, when you view there site it looks fine, but they give 100+ errors. For some reason, errors seem to show up more in tabled layouts. You will see a site design in all tables if you view their source and there is nothing but <td><tr> on the page. It is okay to use tables for some specific modules or only partially when needed, but to make an entire layout on tables in not intelligent design at all.
Enter CSS
There are many ways to design a website effectively. With CSS, the tableless layout can be very flexible. One line of code can change the page layout completely. And this is a good thing, because once tables are placed, you have to go back into the html just to change it. Having designed all my layouts using external style sheets I can say that it does take more time and you will get a bunch of headaches. Usually the headaches will be from how much we all hate IE and why does everything look different in certain browsers. But the more time spent on a tableless layout, there is less time for modification in the long term.
Still don't get it?
Someone asked me when I was talking about css. They were like "what's that?" There are probably many analogies. At the time, I gave an example of a solar power plant. Think about the new age solar plants and the old school plants. At ASU you will see rows of solar panels that probably are stagnant and don't move with the sun(though I am not sure). Now look at the newer power plants that have rows of mirrors that reflect all there light on a single tower that contain the solar panel(s). My point is irrelevant to which produces more power, but more relevant towards time. Imagine 10 years down the line when nano solar panels come out and produce 1000 times more power than today's. Well, if you have a grid of solar panels (old school method), you have to switch every single row out and replace it. With the other method, it would be way easier to change the single or group of panels that are centrally located in the tower.