Your computer monitor, LCD flat panel or otherwise, is arguably the most important part of your computer. It is the only way you can receive information from your computer, and since computers are all about information that means a problem with your monitor could be a big problem indeed. But what many people don't realize is that when it comes to computer screens, bigger is not always better. In fact, it's not even necessarily better with televisions. Just as there is such a thing as "too small", having a screen which is too big can make viewing it an imperfect experience and even physically uncomfortable.
What size is best depends largely on what you are doing. Take for example someone who is just browsing the web and checking email. Such a person uses their monitor almost exclusively for reading. Books and paper can be manufactured in any size but yet we don't see super-wide books or print our text documents in landscape mode. When it comes to reading we know our eyes prefer to go left-to-right (or vice versa for some languages) so far before it becomes uncomfortable or difficult to read. That means someone who uses their monitor mainly for reading would do better with a smaller monitor. One other option that might work well is one the latest styles of wide screen monitor, which swivels to become tall and narrow -- almost the shape of a book page, making it the perfect monitor for reading.
For people who watch movies on their computer, the problem with too large a monitor is your eyes can only see so much of the screen. This of course depends on how close you are to the screen but as a rule if a screen is taking up more than half your field of vision (the monitor not only fills the center of your vision but also some or much of your peripheral vision) then it can be difficult to see what is going on. For video gamers this becomes even more of an issue. Of course you want an immersive experience, you want to feel like you're actually there, but if you have to literally turn your head to see another player at the edge of your screen then you are not going to enjoy the game very much, or likely to have much success.
As a general recommendation, a 19" screen is likely plenty for someone just checking email, 23" for the gamer and 26" for the movie enthusiast. These are somewhat arbitrary and open to interpretation, but when selecting a monitor use them as a guideline and keep both the pros and the cons of larger LCDs in mind as you shop.
