Signal transduction. Are there close encounters between signaling pathways?

Do different signaling pathways inside the same cell talk to each other? Evidence suggests that in the worm and fly, signaling pathways exist as separate linear cassettes, whereas in mammalian cells there does appear to be cross talk between signaling pathways. However, as Noselli and Perrimon argue in their Perspective, most of the evidence in mammalian cells comes from tumor cells and overexpression assays. They suggest that true cross talk may not actually exist in mammalian cells under normal circumstances.