I've been using the format of the LJ icon like graphical Haiku. The 100x100 pixel and 40K file size limits are like line counts and syllabification. But an LJ icon, like a Haiku, has non-physical constraints. Mine have stories behind them. They're puzzles. They relate to the dual audiences of my close friends and random strangers on the net. I'm sure I could find other threads to tie them together.
I wonder how you'd formalize the stylistic aspect of the LJ icon art form?