Another thing that's very noticeable while exploring the
Posterousphere (sorry) is that the site's developers are listening to
the users. I emailed them a question and they responded very quickly.
They also post comments on user sites where appropriate.
 
A short amount of searching showed me that they plan to add per-site
Autopost settings soon (so you can have more than one Posterous, each
with different Autopost options), as well as support for Markdown
(which would be a huge improvement, in my opinion).
 
Edd said that "Posterous gives me warm feelings":

http://bitten.twiceshy.org/posterous-gives-me-warm-feelings

and I see exactly what he means. It feels natural, useful, and easy.

(That paragraph there is why Markdown would be good.)

Another unexpected thing: the total lack of template customisation
feels like a good thing! Less for me to fiddle with. What's there is
simple and works.

Posterous has a nifty feature whereby it can automatically re-post
your content to your other sites and social network accounts. Now the
last thing I want to do is have everything I post in one place
automatically appearing in others, but Posterous does offer a certain
amount of fine-grained control that can come in useful.

 One way I've found it useful is for getting content into Wordpress by
email. Now, in theory, Wordpress has this feature built-in, but in my
experience it's a pain. You have to provide Wordpress with a mailbox
of its own, that it checks periodically for messages. I've tried
several times, and never got it to work.

 Now Posterous takes that problem away. You can set up a Wordpress site
for autoposting, and then make use of the fine-grained control to
ensure that only the right stuff ends up there. So, if I want to send
a photo to the Bradford on Avon blog via my Posterous account, but
*not* have it sent to any other services I might have linked Posterous
to, I can do so by emailing #text@posterous.com, where "text" is a
string of characters found in that site's URL.