In recent years, the monitor size has grown and grown. Now, when you go to your local electronics shop you find monitors that look larger than big screen tvs.
Years ago, this would have been a nightmare to web designer / web developer. However, nowadays, browsers like Firefox 3.x and Internet Explorer 8 do a fantastic job at holding decent resolution when someone zooms in on the webpage. In Explorer, the commands are Page >Zoom >Pick a Setting and in Firefox View >Zoom >Pick a Setting.
Therefore, designing pages these days to look proper in various computers is quite a challenge. But, still, it normally is broken down into two parts. The severe minorities that use phones, Blackberrys, Iphones to surf the web and those that use a laptop and a desktop. The portable devices normally are less of a concern because browsing the net with those devices and typing is a real pain and an eyesore. I bought a top of the line phone for this reason and have downgraded its usage only for checking email and perhaps MSN messaging on the fly. Otherwise, it is totally the wrong tool for web surfing unless you are into the social media thing that caters to chatty this and chatty that. Anyone that is dedicated to surfing would use a laptop or desktop. The extra price is worth every penny.
Catering to the larger screens is still quite a mission. What size should that website be? Well, a safe size is to fit tight into 15" monitor and fit into everything above. You could go narrower. As far as length goes, if the top half looks good in everything (like a well figured woman), the fact that the bottom lingers a little off the page and must be seen by scrolling is fine; at least in terms of style. A site could be made short in length if you want all the page to fit into any monitor. However, the short page will look a little tiny to the big spender with the large monitor. This is really a matter of choice at this point, but after looking at laptop sizes in the stores over the last two years, the sizes 15-17-inch still seems to be the most common sizes. A laptop larger than 17-inches is a little bulky to carry around. Consumers have been quite happy with the common sizes that have tendd to dominate the market in 2009.