What I found was that I could make exposures two or three stops below what my meter recommended and still get good color. However, the images resulting from such low light conditions allowed very limited enlargement. Beyond about a 600-pixel width the grain starts to resemble baseballs. Going in the other direction, though, both the color and the grain structure held up well past the film's rated sunny day limit.
Part of my inspiration to use the Fuji 400 film came from seeing some recent work in the Flickr vuws group by a fellow who calls himself UkrainianSensation.. His picture of the Golden Gate is really an extraordianary example of the capabilities of the little ultra wide.