I can only spread rumors
from many discussions about the troubles introduced by recent Picasa 3.9 updates (latest is 137.69 in December 2013), but there's lots of discussion about how it introduced some huge new problems. That's my experience, which is why I think Google either doesn't care about the desktop app, or wants to push users to its online photo system. Rumors say the update is mainly to benefit Google+. After six months of driving users crazy, there's no sign or even promise of fixing the new problems, per statements by Google insiders on their own forums.
This update broke lots of syncing because it forbids duplicate tags in photos (montage, or person and photo of person as happens in homes, or simply mistaken tagging), and apparently even overlapping tags (two faces very close together). Syncing simply fails, silently unless the user notices the sync symbol of an album changed, gets suspicious and digs in, with no help from Picasa -- once spotted, the error message is mysterious, it doesn't identify what photos need fixing, and rather than skip the problem photos it prevents the entire album from synching. Not a very helpful "update".
Also, Google+ implemented and set by default that photo enhancement would be active, and added Auto-Awesome photo processing, yet apparently this confuses and blocks some syncing too because it alters only the Google+ photos, not the Picasa photos. (I can't verify this since I have, I think, disabled all Google alteration of my photos, though it's a very clumsy procedure.)
Further, Picasa sharing control has a checkbox to email others who are in face-tagged photos. It used to actually control this, but a recent update now forces everyone to be emailed, all the time, ignoring the checkbox, driving everyone crazy. Google wants to pull everyone to Google+ so they simple force emailing in spite of the user's preference.
Then there's the infamous new error message "Please check that you are connected to the Internet", often reported when trying to upload or sync an album or folder. Huh? It's never an Internet connection problem, but that's what Picasa declares. My hunch is, too many files in the batch or perhaps the collection, but without an accurate error message, or even better, actual docs on what is allowed/forbidden, the user is left hanging.
Also, this update installs Google+ Auto Backup for the Desktop, which then sucks up bandwidth and Google Drive storage space, separate from Picasa's uploading. For the few users who pay attention, they can control this, but most people just click through. Besides, it is presented as a Picasa feature, though really it's a separate app. It seems to be Google's version of Microsoft's clumsy attempts to force Skydrive/Onedrive on Windows users, and/or to get users to pay for additional Drive storage. It would be straightforward for Google say that Google+ is the way to backup Picasa photos, but instead they are limited in size while Auto Backup is not. After considering the tradeoffs, seems like the user only needs one of these but both are packaged in Picasa. Goofy.
Etc, etc. I don't mean to start a debate, just supporting why I think MC has such a big opportunity as Google ratchets up the many ways it disappoints its users.