Even more important, right now Lytro picture libraries cannot be merged at all. This comes into play if you ever delete a given batch of pictures from the Lytro camera before you remember to import those pictures onto all of the computers you're using, since at that point the libraries on each computer will no longer contain exactly the same pictures.
IMPORTANT: If you realize this soon enough after it happens, you can just backup the more complete Lytro Library to your other computer(s)-- libraries are interchangeable between Mac and Windows. However, If this happens more than once, such that your Mac ends up containing sets of pictures A and C, while your Windows machine contains picture sets B and D, and the camera has had any of those pictures deleted from the camera, then right now there won't be any way to combine all those pictures into one library. In that case you'd have to switch between two (or more) Lytro Libraries manually in order to see all of those pictures on the same machine.
Therefore, you will want to be very careful about moving or backing up a library from one computer to another-- you may want to verify exactly which sets of pictures are in each library first-- and to be even more careful when deleting older libraries. Keeping different libraries in specially labeled folders may help you keep them organized.
Perhaps the easiest way to keep all of your pictures in one place for viewing later is always to upload pictures to Lytro Web right after you import them onto any computer you use. (We offer privacy settings in case you don't want others to see certain pictures.) If you care about seeing as much detail and refocus potential in your pictures as possible, though, then be aware that Lytro Desktop still has a significant advantage in those areas.
IMPORTANT: Since pictures uploaded to Lytro Web do not contain all of the data in the original light field picture, be very judicious about deleting pictures from Lytro Desktop on any computer, whether they're up on Lytro Web or not. Also, be aware that even in data-compressed Lytro Web format, it is not currently possible to download pictures from Lytro Web at all, nor to import pictures into Lytro Desktop individually.