Bridge is a image/asset browser and its organizational skills very basic. Uses ACR for RAW conversion and it is destined mostly to be companion to Photoshop.
Lightroom is design to be an organizational tool to help photographers quickly organize, select and edit images. Then quickly correct the images and output them be it via printing module, web module or even with very basic presentation skills that you can use to show your clients the images. It has many tools that Adobe ACR does not have.
It is design to reduce your trips to Photoshop.
With version 2 you will be able to do localized image corrections and work with two monitors.
If you are a photographer that has to quickly navigate trough thousands of images, like wedding or press photographer, Lightroom is the right tool. If you are a Fine Art photographer, for example, you may be able to do without Lightroom, but still, Lightroom will help you organize and search through all your images, something that Bridge wasn't designed to do.
One of the biggest strength of Lightroom is the Global presets. They extend the LR power from a strictly correction tool to a creative one helping you to do quickly things that you could only do in PS before.
My suggestion,
download the trial version of Lightroom beta 2 and play with it. I believe you will quickly discover that you will fall in love with it. You can extend the trial period if you get one of Lightroom current users to "invite you" to extend. There are plenty here that will be happy to "invite" you to extend. Let me know.