Let's say you have a bunch of raw files adjusted with Adobe Camera Raw, and you want to make a load of JPEGs. It's not a novel nor a difficult task - Lightroom's export function is designed for the job, or if you're using Bridge you might reach for the Image Processor which runs the files through Photoshop. Another Bridge-based solution would be to open all the raw files in Adobe Camera Raw, select them all and hit the Save button.
In each case, your poor computer is having to create the JPEGs by processing all that raw image data. But because it is doing so, you can at least be sure that the JPEG output does reflect all your Camera Raw adjustments.
But it is not quick, and it is a pain when Lightroom or Bridge has already done the hard work of updating thumbnails and previews (particularly when you think that Lightroom now updates Bridge's Camera Raw cache).
A new option is Bridge Export to JPEG (it's called BridgeExportToJpegCS4), a script by Adobe's David Franzen which he has significantly extended for Bridge CS4, adding presets, metadata and colour profile options. Its beauty is that, rather than reprocessing the raw images, the script uses the previews which Bridge has already rendered and stored in its cache. So, if you already have updated thumbnails and previews, it's light years quicker than the other options.