I am using Ubuntu 12.04 LTS on Lenovo T500 with Gnome desktop.
I have to upload photos daily for work and 2 weeks ago lost thumbnails and the ability to select preview. I assume an update did 'something'. Settings are correct to show thumbnails always and I've increased the size, but all I get are miniature boxes in my upload window.
Frustrating having to right down jpeg numbers and go from there...
rm -rf ~/.thumbnails
Then try to restart. – Chester Oct 10 '13 at 8:06