Here are some reasons why I use Posterous.

How did I discover Posterous?
I stumbled upon Posterous when Google-ing for a blogging site that posts via
email. I spend most of my time at the office and corporate firewalls can be
a b****, blocking most "social sites" thus updating via web is, at most times,

impossible. Email, however, is accessible. Since the primary medium of
Posterous to make posts is via email, blogging (from the office) has never
been easier.

Why is this good?
Blog creation on Posterous is by far the simplest I've personally done. Just
send an email to post@posterous.com and you have yourself a blog! It's just
like emailing a friend (who's outside the corporate firewalls) and asking
the friend to post to your blog on your behalf -- only that it's done
automagically with, I assume, no human intervention.

Other blog hosts can post by email, why is Posterous any better?
Yes, other blog hosts can post via email. But as I mentioned, posting via
email is the primary medium of posting in Posterous. Other blog hosts (those
which I have tried) need you to remember a weird email address (which you
personally set-up) which can be confusing at times. With posterous, it's
basically post@posterous.com -- how much straightforward can that be?

Other cool things about Posterous?
1. The simplicity of adding photos (and other file types) to your post via
email attachment.
2. The availability of inserting page breaks and using Markdown, among other
things, in posts created via email.
3. The ability to customize your site's theme, HTML and CSS.
4. The discreetness of composing a blog post in an email client (i.e. email
client I use in the office) so that people who pass by think I'm writing an
email (and not updating my blog).

Posterous has actually made me a different blogger. Because now, whenever a
thought comes to mind which I think is a good blog post, I just create a new
email message and send; unlike having to postpone it later when I get a
chance to post via web, which almost always results to a lost or forgotten
post.

Pax Vobiscum.
~ Eric
http://riclags.posterous.com