[jrnkntl]

It is a namespace thing. I am pretty sure. When I use a title for my posterous posts that no one ever used before, the permalink is just the title. When I for example post something titled generally like "photo" it becomes "photo-73864"

[codeflo]

So all post URLs share a single global namespace, regardless of ownership? That's not a very clever design IMO.

[jrnkntl]

yep, looks like it.

if you check for example: http://posterous.com/explore You can see all pretty unique titles without a number appended and then a post titled "Tetris" gets "/tetris-194"

Even if you post something without a title it just gets an ID assigned which is (this is a guess tho) the unique ID in their database of all blogs.

[rantfoil]

This is changing soon! It's on our roadmap.