This is a boon, especially to people selling intellectual property (think local band w/MP3's) over the internet. If you have already bought something from Amazon, making a donation, or paying for something should be pretty easy since it uses the same 1-click backend as the rest of Amazon's site. From reading the FAQ, I'm not quite certain how the details of Amazon's system differ from PayPal.
Interestingly, in addition to the "Pay" button, you can also go into your Amazon account and "UnPay", with no questions asked. It makes sense that in a voluntary system you can change your mind, and was a welcome surprise while reading their FAQ.
The processing fees which Amazon charges are quite high- a flat $0.15 fee in addition to 15% of the total donation. For $1, that works out to 30%, and for the maximum $50 transaction, it's just a little over 15%. When handling credit cards for business transactions, the standard fee works out to be ~3-6% (this is the same rate what grocery stores and computer stores pay when customers use credit cards), so Amazon's 15% processing fee leaves plenty of room for profit.
Contrast this fee to setting up your own secure web payment system (with account management, logins, etc...) and the extra 10% in processing fees is definitely acceptable for small websites. Plus, for most small websites, Amazon's number of registered users with credit card dwarfs the small website's userbase, making the probability that a user can pay under this system
With tip jars, Amazon's new honor system, and even Stephen King's online book released under the honor system, it seems like the people are trying to use the web to voluntarily collect money for their work.
However, fluffy's tip jar is empty, Stephen King has made a paltry $0.5M from his online book, and the featured site for Amazon's Honor System (icebox.com) is closing.