I've just learned that after copying lots of big photos from my Lumia 1020 to my network storage device Live Gallery won't load them anymore. Just lots of gray boxes! Just a little bit of searching brought me to a Microsoft support page that provides instructions on how to fix it. Very easy fix, though the specific registry location has changed since the article was written. You actually want to go to:
HKEY_CURRENT_USER\Software\Microsoft\Windows Live\Photo Gallery
to create the MaximumFrameSizeMegapixels key. Other than that, it works like a charm! This only seems to matter for network images. When the photos were local I never had this problem.