I interviewed with a very well known company in these circles. I was delighted as they are known for paying attention to the everyday aspects of running a business & being open about it. (It was actually my 2nd time applying & interviewing with them. I didn't hear back that time either, having had a Skype interviewed with the founders).
However, I was more than disappointed that after two interviews with staff members, personality test and contact from the CEO that I was in the final shortlist - a month long process - I never heard back again. The only way I knew I hadn't been hired was once the new hire was announced on the company blog.
Between the creative application they'd asked for, interviews & tests, I'd put in a couple of full days of work. Being rejected would have been fine, understandable, but never letting me know was disrespectful & goes against the culture they project.
A few weeks later, the same company advertised the exact same position again on their blog, as I believe they wanted even more coverage than the first person they hired. I decided not to apply that time.
All in all, a simple 2 line email thanking me for the effort and letting me know would have sufficed. Over a month of waiting for an email to drop was painful.