Lightroom 5 has been released... see the announcement at Adobe.
There's a bunch of new stuff.... a good place to start your own investigation is Victoria Bampton's “What's New in Lightroom 5” and “What's New in Lightroom 5.0 Beta” articles. Also, Sean over at Lightroom Blog is keeping a list of tutorial/review links.
The most exciting new things for me are “Smart Previews” (I can work with my entire 130k library of images on my disk-starved laptop), “Upright” perspective correction in Develop, where I can easily correct for my bad habit of not holding the camera level, and the new advanced healing brush, to paint away things you don't want in the image. I also like the new True Full Screen mode.
Warning Warning Warning
One thing I don't like is a very dangerous Publish-related bug that remains in the final 5.0, that can cause you to delete your master images without even realizing it!
The problem is that the selection shown in a Publish Grid may not be the actual set of selected images, and so when you intend to perform operations (update metadata, delete images, export, etc.) on what you see as the selected images, it might not happen... a completely different set of images may be affected (updated, deleted, exported).
In my eyes, this is just shocking. This screenshot shows the problem, using the Publish Collection for my “Selected Blog Photos” gallery on Google Plus as an example:
The selection shown in Filmstrip is the actual selection... it's the selection shown in Grid that this bug causes to sometimes be wrong. In the example above, the two water-polo shots of my 10-year-old son are shown as selected in the Filmstrip, and they are the ones that any operations will actually act on, yet in Grid, six unrelated images are shown as selected. They are not actually selected, and invoked operations will not act on them.
The moral of the story is:
In Lr5, never select images in Grid in a Publish Service.
Even using the next-image arrow key does not properly update the true selection, though it does update in Grid, making you think everything is working fine. It's a very dangerous bug.
It's best to avoid working in Grid in Publish until this is fixed, but if you must, be sure to do so with the Filmstrip also open, and use the Filmstrip to make and identity selections.