Want to know what percentage of your users see that "buy now" or subscribe button? If you're selling something, you should be interested in that. If you sell or buy advertising on a blog, you'd want the advertising to be seen by majority of the visitors too.
Whatever the most important element on your page is, you want to make sure it is above the fold, which means what the user sees when they first enter the page. So no scrolling or anything.
Because many users leave if they don't see anything interesting, check that your call to action or something eye-catching is in that first view. And with that, Google's new browser size tool will help you.
Google Browser Size is a visualization of browser window sizes for people who visit Google. For example, the "90%" contour means that 90% of people visiting Google have their browser window open to at least this size or larger. - How browser size tool works
With this tool you can ensure that majority of your visitors see the most important parts of the page. If a important element, like "buy now" button is only visible to 80% of the visitor, that means 20% of the visitors cannot see it when they first enter your page.
It's free and it's very easy to use: Just enter your URL at http://browsersize.googlelabs.com/ and you'll see nice visual like this:
Browser Size tool will show you what your visitors see when they enter your website, depending on their screen / browser size. The tool shows what percentage of the users (on average) see what.
For example from the picture we can see that ~90% of the visitors to this blog see the "follow me on Twitter" button, but only about 80% of the visitors see the whole RSS Subscribe icon.
Check out the Browser Size tool at: http://browsersize.googlelabs.com/
Here's hoping this will help you find the right place for the most important elements on your blog and perhaps gain extra subscribers, or even better, more sales because of checking the design.
Source and more information: Google Code Blog - Introducing Google Browser Size