Kind of an old topic, but I needed to do this today and I was hoping to add a bunch at one time on the site...unfortunately just 1 at time still. So here's my work around, I have a list of almost 200 that I wanted to put in a bookmark list. Step 1: create the list on geocaching.com. Step 2 using Project GC virtual GPS, I can add that list of 200 or so with a simple copy/paste. Step 3 Project GC Export feature....you can Export to the existing list you made in Step 1. relatively painless.
Mike