Cascading Navigation?

[RingingPHoneML]

Designing a new site and have a question about navigation. I have seen scripting used on sites in the navigation. When you mouse over a word and more related sub-categories show. I am not talking about flash though, and I am also not sure of the technical name.

Here is my question, is there any data showing that users don't like the use of that or that they prefer it?

I have a few large categories, and a lot of sub categories that I want to try to show throughout the site. Any other suggestions?

Thanks.

[AshInVegas]

This is usually done using JavaScript, which can pose problems. Since 10% of users either have browsers that don't support JavaScript or have their JavaScript turned off, it's important to offer users an additional way to navigate that isn't so reliant on the technology. In other words, don't rely ONLY on JavaScript navigation.

Also, in usability tests I've done, users with laptops had a much more difficult time with these JavaScript menus due to the inexact nature of the touch pad (compared to a mouse).

[LazyJim]

A big help for lap-top users and other users who may have less motor skills, ensure the whole rectangle in which text appears is clickable rather than just the words. As a rule, and pretty obviously, the bigger the target the easier it is to hit.
Try experimenting with this CSS: a {display: block;} but only apply that to the <a> tags in your expanding navigation menus.

As Ash pointed out, the most important thing is to ensure the site can be navigated easily when the expanding menus fail for any reason. You have two easy options for this:
1) have the whole two-level menu expanded initially on the page and use JavaScript to hide the second level (and then show each one individually as the exanding menu system you described). Tis way if JavaScript menus don't work on someones machine, then JavaScript also will fail to hide the menus in the first place, leaving your whole navigation system visible.
2) use <script> tags in place of your menu with a functions that dynamically write the menu code into the page. After the <script> tags add a set of <noscript> ones, inside which is an alternative menu for browsers that have no scripting ability enabled.

[RonBurk]

is there any data showing that users don't like the use of that or that they prefer it?

You may find this study of interest.

Also, the following anecdotal data point. The last time I did a detailed site review of a website using cascading menus, I reproduced (with screen shots) a half-dozen distinct UI bugs within 15 minutes of testing. These were things like leaving a menu item high-lighted even though the mouse was long gone, highlighting the wrong menu item, instead of the one the mouse was actually over, leaving a "ghost" menu item image because of a redraw failure, bugs related to failing to handle loss of input focus correctly, and so on. One wonders what users think when they encounter such behavior.

Cascading menus seem like a simple thing to code, but they are in fact quite tedious to get all the bugs out of.