It looks like Google decided to simplify things as much as possible. They just took the original Picasa for Windows and made it working on Linux with Wine (it is included into the Picasa Linux distribution). So, it is really not a true Linux version. But due to stability of Wine technology (see my “Wine and Photoshop” post) it seems to work well.
At first view, Picasa provides the same set of the photo organizing functionality as digiKam. It supports the same faceted photo collections organized by folders, timeline and tags (“labels”). The only difference is a distinctive feature of any Google product – the search box which is always presented in the program window. The photo editing functionality is also similar to the default set of digiKam tools. But the rich set of digiKam’s additional plugins makes it image processing functionality looks more professional, while Picasa supports only a basic set of simple and most needed image fixes and effects. Many of them are automated and lack some fine-tuning but in general, they should be suitable for the most of non-professional photographers.
And, as it was expected, Picasa doesn’t import photos to Flickr – perhaps by understandable (competition) reasons.