Some random ideas to salvage your idea a tad (which seems to be very difficult to make work given it's difficulties):
* Start with a niche like used books and perhaps partner with a book swapping site (e.g. bookmooch or bookcrossing or something) to get the initial tests done on something people don't mind losing. Other second hand material would be good, too.
* I think you'd also do much better with such a service if you treat your site more like a craigslist for "package hitchhiking" and reverse the process.
I.e. travelers post where they're going on their next road trip and they say they're willing to take a few odd things. So you'd get a lot of random trip listings perhaps all on your front page until there's enough to break them down.
People browse the site when they have something to ship (especially second hand stuff, etc) and if they see someone going the way they need, they make a bid/offer to the person going that way.
* On the security angle you might look into the "friend of a friend" and "church group" organization like http://www.goloco.org does. Targeting widespread organizations or friend networks may make this more palatable to people worried about trust.
* Posting some examples of "what people shipped" on the page, with a constant stream would help people feel more comfortable.
* I assume there will be ebay like ratings and reviews, etc?
* Overall, I'm not sure this "disrupter" is going to work unless you can plug it into the thriving secondhand market as an extremely thrifty for low-value items. Positioning yourself initially would do you a lot of good.
* Finally and not most importantly, the website (unless owned by craigslist) will need a much more polished design to make people thing this is a "real deal" enough for them to try it out. I don't think that alone will help you, but your traction issue isn't going to be helped by your current design (usability and visually).
Best of luck-- regarding the other comments, sometimes the naysayers on Hacker News are wildly wrong and harsher than they used to be, but they often have very good points that will let you adapt your vision and save it. Take all the advice with a grain of salt. You're going to learn the best from your users once they start giving you feedback, so testing your idea and site is far more important than our responses.
Edit: To that end, give something like feedbackarmy.com a try a few times and see what random people think about the idea and see what percentage you could get to say they'd give it a shot.