Most fellow SuiteScript-ers are aware that NetSuite is built on the EXT-JS library. With that, a broad range of custom actions have been made available for use on NetSuite to improve look & feel of pop-ups, perform animation and monitor progress of complex operations. Here are a few basic features of EXT-JS and how it can be used on NetSuite.
There are operations like complex saved searches that take longer than expected to load on NetSuite. Why not load a progress bar to keep the user informed?
Note: EXT-JS libraries cannot interrupt the browser UI thread the same way a native alert box does. If you wish to use the above, you need to ensure the correct conditions are applied in your code.