I just glued the backpacks on my Thousand Sons last night. I'm presently in the stage of miniature painting that I hate: Touching up details.
There aways seems to be some little detail that I miss. For example, after painting gold on the bolters, I switched to paint the tubing on the backpacks, helmets, and chests. The I noticed that there were some spikes on the legs of one guy that I missed. So I had to go back to my gold still on my palette before if dried out and paint these tiny little spikes. I did that and then realized that some of the Thousand Sons shoulder pads and bolter arms have tiny jewels on them. Now what would have been the easiest thing to have done was paint those when I painted the eyes since they're the same color. Now I have to pull out my seldom-used greens to paint some jewels.
Ok enough complaining! I'm almost done with my first squad and I couldn't be happier.