The no-signup is really good ! It would be even better if you added client-side encryption and a rudimentary support for folders. The use-case I have in mind is sharing photos of an event: there may be a ton, we may want to organize per uploader (so as to not mess up with names) and I'm not totally comfortable with all my pics being in clear on Amazon's servers.
A quick test showed that content was sent in cleartext, directly to trunked's s3 bucket, and then some metadata is sent to trunked.me. Maybe that metadata is encrypted ? Anyway, the content does not leave your browser encrypted.
Neat otherwise !