When I first purchased Adobe Creative Suite 4, Web Premium, included was Adobe Bridge CS4. According to Adobe, the product Bridge is "powerful, easy-to-use media manager for visual people, letting you easily organize, browse, locate and view creative assets." (source: Adobe web site) So I started to use Bridge to organize my (then) hundreds of photos.
Then I scanned in thousands of photos in my film library from a decade of shooting rolls of 35mm film. I started stalling in Bridge, I could not keep track of where everything was. I was losing the work-flow battle. Then I heard about Photoshop Lightroom 2. Once again, according to Adobe "… Lightroom 2 is essential for the digital photography work-flow needed now. -from one shot to an entire shoot. " Lightroom however, was an extra cost stand alone program that cost around $ 250 list.
Well, I read the ads and the reviews and quickly decided to jump on the Lightroom bandwagon. The question is, do you need Lightroom? In my mind Lightroom 2 is meant to be an integrated, but stand alone application for the serious photographer. With Lightroom you can organize your images with catalogs and collections in a much more efficient manner for large volumes of images.
If you are shooting in RAW format both Bridge and Lightroom have the same RAW controls. A little know fact is that the "Develop" module in Lightroom is identical to the RAW formatting controls in Bridge. Lightroom's "Develop" module takes other photo manipulation much more than Bridge. While not as powerful as Photoshop, I find that most of my photo editing is now done in Lightroom and I use Photoshop only for the really heavy lifting. In some cases you could use Lightroom instead of Photoshop or you could even get by with Photoshop Elements or no other photo editing software.
With Adobe Bridge you can organize your photos, you can tag (keyword) the photos and videos. And Bridge can read and write RAW files. With Lightroom 2 you can organize your photos, keyword them, and you can import from a variety of formats and write back out in multiple formats. Lightroom is weak in the area of ??videos. It is more powerful in its ability to "develop" or to modify and edit a photograph. It edits in a non-destructive way that retains the original format. Lightroom is designed to complement the work-flow of a serious photographer that might have hundreds or thousands of images to process or edit, even if it is for a simple crop and format to a print size.
So, the bottom line is that I would recommend Bridge for a person that has some of the Adobe suite of products and needs a lower level of photo organization. I would recommend Lightroom 2 for the intentional photographer, those shoot hundreds or even thousands of shots and needs to organize, edit, print and showcase their products.