Designers & Interface Developers: You may have 24" monitors and your users may have 20" monitors but most will not have their browser maximized to that. Remember that there are two folds on every page: a horizontal and vertical one. Your users will not appreciate resizing their browser or scrolling down and left/right to see your content. If most of what they see above the folds are ads and/or navigation or logo then it's unlikely they'll stick around for long. If they need your service they'll do it begrudgingly and won't speak favorably of you to others. You may get their first ad impression, but they likely won't be repeat customers so ultimately you'll lose out.
Remember the fold.
PS: Also don't make 15-25% of the area above the fold (their browser window) stickied to never go away, especially if it contains practically no content or very little they actually need at any given moment.