I pretty significantly curtail my users' signatures. Text size no greater than 4, no images, no embedded media... Can't remember my character limit offhand, but basically I want it to be pretty rare that a signature takes up the same or more room than a post does. Sites that let the signatures run amok drive me bananas - why do I want to read a two word post, but then a 20-line (or hundreds of pixels high) signature image?
And yes, I know I can usually turn them off... but I don't want to see no signatures. I just don't want to see annoying ones.