One thing I'd been running into with using listingninja.com recently is that it was hard to share my listings. I tried to make an interface that gave users a lot of control over what other users could see, but it was just too complicated and required too much effort from the user.
In the latest version of ListingNinja, realeased today, to share your clipped listings, you can simply send your friends your listingninja.com url. Here's mine:
http://listingninja.com/users/1. You'll also notice (if you're using a modern browser) that there is now an atom feed of your clipped listings, so your friends can subscribe and see what you've been looking at on craigslist.