There is no doubt that Twitter is one of the hottest thing online right now, and it is addicting. Some people like to use a simple pattern, some with their contact information on it. In order to design a background that works best for you, you need to know at least how the mechanic works. Twitter ‘s content area is 440px wide and always horizontally aligned to the center of the screen. What it means is the content areas will float to the center depending on the viewer’s screen size and resolution. Proposal Writet Adam Plitt‘s Twitter is a good example, and indeed very well thought out.
This is how the background looks on 1024 x 768 resolution
You can see his background with him holding the content area fits perfectly to the screen on 1024 x 768 resolution, which is what most people would be using these days.
This is how it looks on an unusual 1440 x 900 resolution
And you can see on the right size of his background, the content area covers his left hand slightly because the background is not designed for a widescreen monitor like the one I am using with 1440 x 900 resolution.
Adam actually really put a lot of thoughts in when he designed this background, and you will know why in a second. I downloaded his background itself off the Twitter and know that the image has a split on the right.
This is because the image background is designed for 2 different, but most common screen resolution, 1024 and 1280 in width. It can be tricky when it comes to design Twitter background, because you will never know what resolution of people are using. The only thing you can do is, know your audience, and design it with a certain demographic in mind.