[eluser]kanjimaster[/eluser]
Stylesheets should be in the html header, so however many you have they shouldn't be being loaded with each view.
Whether you have one or many depends on the relative importance of maintainability and performance. Different stylesheets dealing with different parts of the site may be easier to maintain, but each requires an HTTP request from your visitors' browsers causing slightly slower page loading.
Personally I lean towards using LESS and then pre-processing, concatonating and minifying them into a single file to get the best of both worlds and there are several codeigniter sparks that can manage this for you.