I just finished a nice little edit of two days biking on Galiano Island. It is embedded at the bottom on my blog post linked here;
http://www.somegood.ca/Site/Blog/Entries/2009/9/19_Gulf_Island_Biking.html
There are some very nice trails scattered around most of the islands, many with some nice views and ridges. However, the most unique aspect of riding in the Gulf Islands is some of the low tide possibilities. The sandstone can make for some very tacky riding similar to what I assume Utah's slick rock must be like. You just have to make sure you don't get too low or the barnacles and algae will get you.
cheers