In Lisbon, walk/don't walk signs are mostly decorative. The real rule for crossing the street is look both ways and cross when safe. There's no requirement that you use a designated crosswalk. As long as the coast is clear, you can cross the street anywhere. When my host for the conference accompanied me to the conference center, we crossed the street and my host pointed out, "You know, we're actually using the official crosswalk this time."
I was talking with one of the faculty members of the computer science department at IST and mentioned that in Seattle, the police issue tickets for crossing the street incorrectly. The faculty member responded, "In Portugal, there is no such thing as crossing the street incorrectly."
(For what it's worth, people in Madrid restrict themselves to crossing at crosswalks and generally observe the walk/don't walk signs, although if the light says don't walk and there are no cars anywhere nearby, they will cross anyway. This evaluation of Madrid crosswalk behavior is probably skewed by the higher concentration of tourists.)