I generally have a ton of websites open in Safari (on average I would say 35). Obviously this isn't a good idea for numerous reasons, largely it's a waste of space and a waste of memory. I've lately have been making an attempt to cut this down, and I think I have a fairly decent approach. For general items that I would like to read up on or consider for later, I use del.icio.us, usually assigning a tag "todo" or "tobuy." If it's an action item, I use Remember the Milk, a great webapp that handles to do lists and can shoot you an email/im/SMS when something is due. One of its features is that you can attach a URL to an item, allowing myself to get rid of any webpages that are only open to be acted upon at a later time.