I've backed quite a few Kickstarter campaigns (100+ at last count).
Not every campaign meets its goal, but I have a pretty good record.
Sadly, within that record of successes is a whole bunch of people who, for one reason or another, have not gotten around to delivering their backer's rewards just yet.
The oldest of which dates back to May 29th, 2011.
I am fairly trusting, and really put this down to poor post-campaign planning or unforeseen circumstances, rather than anything nefarious.
It does raise a very interesting point, though. Kickstarter really is proving to be a viable means of getting ones work out to the public for indie creators. It is also proving to be an incredibly effective way to get anthology books recognised - something which traditional comic book stores are reluctant to take a chance on (space and cost issues).
However, bad apples will spoil the reputation of the brand if too may people don't deliver, or fail to deliver and update in a timely fashion.
If you are planning a campaign I urge you to plan the post side of things as much as you do the actual campaigning.
Be sure to factor in timings for completion of a project, delivery of any printed materials, etc.
Be sure to factor in the post costs for shipping, and make sure that you find the cheapest and most efficient ways to do this. Printing your own shipping labels and bulk buying things are a great idea. Establish dates for shipping, and plan to minimize your post office trips by doing most of the shipping in big batches.
Stay in contact. Things happen in this world, but a simple update on the (still active) campaign page to let people know that you haven't forgotten about them is invaluable.
If you have production crew dotted around the globe, or are offering sketches from someone on the other side of the country, maybe the "signed by everyone" edition isn't the best idea!
Take care of your campaigners first. If your book appears in Diamond or a comic book store before it has reached the majority of your backers, that isn't a good thing.
There are more things which you can all do to keep the campaign running smoothly after the fact, and it is a good idea to treat your backers like fans, who might very well back you on another project.