Lightzone has recently been updated to version 3.4. Now that I've finally installed it, here is my first pass look.
First thing to say is it doesn't look much different from version 3.2. The major change in interface is in the use and application of Styles. I rarely use Styles so haven't bothered too much with that but the new preview feature is quite nice if you expand the preview pane.
Speed seems quite a bit improved - i ran some editing on a large format scan (190MB 16-bit TIFF) and it clipped along quite nicely, until I came to do a 100% view for sharpening. Lightzone also seems to handle memory a bit better but still loads up the memory when scanning folders.
Other than that, i don't really see any changes. Is it worth the upgrade? If you're a 3.2 user I'd say so. I'll still be using 2.4 as my primary version.