Looks like you don't need a Posterous account to view password-protected content. Just the password. Not true on LiveJournal. (Not a user of either, yet, but this is how things look on inspection. Corrections/amplifications welcomed.)

There are lots of people in my life who I could give a link and a password to, but who I would not ask to make a LiveJournal account.

yeah this was a big deal for us. Most other sites do access through accounts. That stinks. I want to share my family site with my 100 family members. No way they are going to create accounts. But they do know how to type in a password.

Absolutely right.

Here's an additional use case from my world: I'm in grad school & often want to share data and thoughts with various scientific honchos whose time budgets are very limited.

Now I can cc. a Posterous group called "my advisor might be interested" whenever I send an email. When my advisor gets some downtime, he can check this group out. This lets me communicate in a "non-push" way to him -- I don't clutter his inbox with my email, but I do get to keep him in the loop.

Essentially, this lets me create a "soft" cc. semantic.

I've had this in mind for a while, and made some half-baked efforts to roll my own, but trying out your service will be much easier in the short term.

Keep up the good work!

LJ doesn't really have any good rich media processing, especially over email. Also, LJ doesn't autopost to anywhere else.

Though for public blogs, you can autopost from Posterous to your Livejournal.

As for specific friends-only functionality, this is password protected so people without accounts can easily access it.