From DPreview.com:
Adobe Systems Inc today announced an update to Photoshop Lightroom beta with version 4.0. Available immediately for free download, version 4.0 unites product feature set for Windows and Mac platforms allowing a new way to import, manage and showcase large volumes of digital photos. Version 4.0 also adds improved workflow tools including a precision white balance option, new filters and search presets, and a new tone curve adjustment feature
I've been goofing around with this since it first hit Beta and this version is really looking good. It's worth the time to download and check it out.