I messed about with Posterous a few months ago (http://
redduffman.blogspot.com/2009/04/joy-of-posterous.html) and was
surprised that it did not get the sort of attention that Audioboo
recieved at the time. Especially when you consider that all you need
to record, publish and aggregate is a standard phone with a 3g
connection as opposed to an iPhone. I particularly like the fact that
it automatically generates a feed for your iTunes and other readers.
I wouldn't recommend it for large audio files though for the same
reason that Simon gave. I too have not been able to find a way to
upload a file directly as opposed to via e-mail.
However, it is ideal for beginners getting to grips with podcasting
and who don't want to bother hosting their own files. It's also ideal
for mobile podcasting.