A popular topic in interactive design is that of scrolling. When is it ok to scroll? Is it ok to scroll? Will people know they can scroll? What information should be above the fold?
Above the fold
When web design began the designers were mostly trained print designers since interactive design was a new field and "web" designers didn't exist. The concept of "the fold" is one that print designers imported from newspaper design. The goal of designing "above the fold" was to keep the most important headlines and images in the top half of the newspaper so when it was folded in half at the newsstand the most enticing information would be visible and passers-by would stop and buy the paper.
With the internet the concept of designing web pages with the important information above the fold, keeping key information viewable without scrolling vertically, was met with a new challenge: monitor variety. When a publisher produces a newspaper every customer gets the same sized paper. The content that is above the fold for one reader is the same for every reader. With web design the variety of monitors, browser chromes, and resolutions is so diverse that there is no standard height for where the fold begins. The fold on my phone is alot different than the fold on my 27inch desktop monitor. The ipad has not one but two folds: one in portrait orientation but a shorter fold in landscape orientation.
Ignore the fold
People's fear is that important information will never be found if it is below the fold. That somehow people (not themselves of course) don't know how or when to scroll to find additional information so the solution must be to cram as much content at the top of a page as possible. This is ridiculous. Usability tests continue to prove that not only do users scroll but scrolling can actually improve the user experience. If people feel they are on the right track they will continue to scroll for content.
Design pages that are legible and attractive. If your application is well designed it encourages people to explore the document and they will scroll on their own.
Vertical scrolling only. While users can scroll vertically as well as horizontally, generally speaking a page should do one or the other and people prefer vertical scrolling. Vertical scrolling is a more standard method of navigating content as well as the simple fact that most scroll wheels move vertically and not horizontally. Vertical scrolling is just easier.
Monitor Resolution. To avoid horizontal scrolling you should know your intended audience. I use analytical data to find the largest number of users with the lowest common resolution and design for that. 1024x768 is still a decent standard size as well as being the resolution of the ipad in landscape orientation.