Posterous is going to be huge. Even Andy says so.
Over the years, I've used every blogging platform I've found, including (but not limited to) WordPress, Typepad, MovableType, Squarespace, Vox, Livejournal, Blogger and Textpattern. The easiest among those are the hosted solutions, like Typepad, Livejournal, Blogger, Squarespace and Vox (note that Typepad, Livejournal and Vox are all products of Six Apart). WordPress and MovableType are (usually) self-hosted and require the blogger* to create and link to a database.
After installation is complete, they all require some degree of fiddling. Customizing the layout, design, colors, graphics etc. takes time. Adding something like an image gallery is even more time consuming, and often requires a plug-in which you must find, upload, configure and test on your own.
By contrast, here's how you create a complete blog with Posterous:
Send an email message to email@example.com.
Here's how you create a full-featured, thumbnailed photo gallery with built-in navigation on Posterous: Email your photos to firstname.lastname@example.org.
Want to post a video? Same thing. It'll even encode it for you. Send nearly any codec you want.
It's brilliant because there's nothing to learn. Everyone knows how to send an email message and customers can use the email client they already know; the client that's always available via a laptop, phone or iPod. Additionally, Posterous can notify your other accounts, like Facebook and Twitter, each time an update is posted.
The only drawback I found was in updating a gallery throughout the day. Let's say I want to document a trip with multiple photos added to a single post as the day progressed. How can I do that? PicPosterous [App Store link] is the answer. I spent the last couple of weeks using a beta of PicPosterous and spoke with Sachin about it. Click below to read my reaction and conversation with Sachin.
*Some web hosting companies provide a one-click install for WordPress and MovableType. Wordpress.com also provides free and premium plans for WordPress users.