One of the biggest changes I noticed off the bat is that version 4 is 64-bit only and requires a minimum of OS X 10.6.8. For the Windows side of things you'll need Windows Vista or Windows 7. Lightroom 4 introduces Process Version (PV) 2012. From what I can tell it seems that Adobe has focused more on a redesigned layout rather then rendering performance. I need to test for myself but if this is the case I'll be deeply disappointed.
The white balance selector has been improved to allow for more granular selections. This will come in handy and I can picture my workflow making great use of this new feature. Exposure and brightness is now combined into a single slider. The highlights, shadows, whites, and blacks sliders also received minor improvement to their use and ability. Other then that Adobe has introduced a bunch of features I'll never see myself using.
I really wish Adobe, Canon, and Nikon (as well as other camera manufactures) would focus more on still imaging instead of trying to build video support into their product line. Sure, I understand that there's a huge market for those that want a still and video camera in a single package but there are also professionals and amateurs that simply want a good still camera! Either way I'm sure I'll end up paying the Adobe tax. Here goes nothing! =)
New Features in Lightroom 4 Beta
Highlight and shadow recovery brings out all the detail that your camera captures in dark shadows and bright highlights.
Photo book creation with easy-to-use elegant templates.
Location-based organization lets you find and group images by location, assign locations to images, and display data from GPS-enabled cameras.
White balance brush to refine and adjust white balance in specific areas of your images.
Additional local editing controls let you adjust noise reduction and remove moirÃ© in targeted areas of your images.
Extended video support for organizing, viewing, and making adjustments and edits to video clips.
Easy video publishing lets you edit and share video clips on Facebook and FlickrÂ®.
Soft proofing to preview how an image will look when printed with color-managed printers.
Email directly from Lightroom using the email account of your choice.