What are the pros and cons of mixing horizontal scrolling with vertical scrolling?

I'm working on a new site for a company. We are working on a new concept for them, using horizontal and vertical scrolling. We know that the users that interact with the sites are advanced users so a little of complexity in the navigation is not an issue. I wonder what are the cons (and pros) of having horizontal scrolling. What are your thoughts of mixing vertical scrolling (to go between different sections of the sites) and horizontal scrolling (to navigate through the content of one section of the site).

Answer

Jakob Nielsen argues against horizontal scrolling (still actual):.

We know from user testing that users hate horizontal scrolling and always comment negatively when they encounter it. Customer satisfaction is surely reason enough to avoid horizontal scrolling. There are two other reasons as well:

• On the Web, users expect vertical scrolling. As with all standard design elements, it's better to meet user expectations than to deviate.


• When pages feature both vertical and horizontal scrolling, users have to move their viewport in two dimensions, which makes it hard to cover the entire space. For people with poor spatial visualization skills, it's especially challenging to plan movements along two axes across an invisible plane. (Typically, users score lower than designers on spatial reasoning and visualization tests.) In contrast, one-dimensional scrolling is a simple way to move across content without advance planning: you just keep moving down.

Personally I think it's a bad idea to use horizontal scrolling for non-touch devices. You may use some kind of switchers (like next/previous category buttons) and animation to emulate horizontal scrolling, but modern input devices (with few exceptions, like Apple's Magic Pad, etc) still doesn't provide a good experience with horizontal scrolling unfortunately.