Lightroom is my new favorite software. It's not perfect, and on occasion can be downright frustrating, but it also saves me hours of work, which has in turn encouraged me to be a bit more aggressive in my retouching choices.
The best way to explain why it's so helpful is by running you through my work flow. I come home after a day of shooting cat photos at a shelter, pop my SD card into my laptop, and allow Lightroom's downloader to do its stuff. I have a keyword and metadata preset that it automatically applies to each photo, and all I have to change is the name of the directory in which to drop the photos. I shoot simultaneous raw and JPEG; Lightroom loads the raw versions and just copies the JPEG files.
Once downloaded, I scroll through the photos, adding the ones that have potential to a Quick Collection by pressing "B." I frequently have frames for which the flash didn't fire, so as I scroll through, I hit Auto Tone to bring up the exposure and see if these black photos are salvageable. After sorting through all those images, I then filter it to the Quick Collection for further work. For each of the photos, I need to decide whether it's going to my Web site, Petfinder, or both. I make a pass through the photos, retouching for tonality and cropping for aesthetics; this usually takes about two minutes per photo. I then export to one directory using my high-resolution JPEG preset. While that's processing, I go back through the collection, drop out the ones I don't need for Petfinder, then recrop the remainder for best animal presentation. These get exported using another preset, which compresses them and constrains the maximum image dimension to 500 pixels, and drops them in a second directory.
This is both a typical and an atypical work flow--one of Lightroom's charms is you can adapt it to many different processes and can move back and forth almost seamlessly between tasks. There's nothing really new you can do with Lightroom--Adobe Camera Raw has had this sort of nondestructive editing capability for a while--but with Lightroom, it finally feels natural to not worry about saving versions. There are shortcut keys for everything, and you rarely need to go to the menus. Property panels slide in and out to maximize screen real estate.
Though quite strong in some areas, Adobe seems to have had some difficulty conceptualizing the interface for online output. Lightroom can generate slide shows and Web galleries, which Adobe has arbitrarily separated by technology, rather than treating them as different ways of viewing photos: Slide shows are output to PDF, while Web galleries are written to Flash or HTML. Both modules feel fairly undercooked, especially when compared with the options available for print, many of which would work very well for online application, like the extensive text annotations. You can upload the galleries to a custom FTP server, though, which is nice.
Furthermore, most rendering operations can really bog down the software, such as thumbnails for slide shows and especially spooling for print. I find it faster on my 1.2GHz Core Duo laptop than my 2.4GHz Pentium 4 desktop (with the same 1.5GB RAM), which makes sense given how much of it Lightroom does in the background. From a performance perspective, Lightroom is clearly a version 1.0 product.
Lightroom doesn't fully replace Photoshop, even for basic raw processing, because you need Photoshop's Proof Preview for accurate color matching. Basically, Lightroom relies on existing color profiles to map screen to print, with no print simulation view. Grrr. Adobe really gets some demerits for this. On the upside, there are plenty of users hanging out in Adobe forums and plenty of third-party tutorials, tips, and tricks on the Web waiting to help you.
Ultimately, Lightroom is one of those programs you simply have to try for yourself to ascertain how it fits into your work style. What I can tell you, is it's worth making the time to give it a shot.