Why don't you try it out for yourself? The last beta release is still available to download and represents some 90% of the features that will be found in the release...
Adobe Lightroom Beta
Also, Digital Outback Photo has an excellent write-up on Lightroom v.1 and exactly what it brings to the table... you can check that out here
Adobe Lightroom at Digital Outback Photo
My opinion? I'll most likely run Lightroom as my primary in-the-field picture editing application on a laptop, whilst Photoshop will still be the workhorse on the desktop.
The two applications are designed to work together and Lightroom is not intended to replace Photoshop (or Elements for that matter) - rather, it addresses the needs of a different set of photographers... particularly those who shoot many dozens if not hundreds of images each day.