Overall the process of moving from a self-hosted wordpress installation to a posterous blog isn't too tricky.  The setup of the blog on Posterous is really easy and I won't get into that here.  There is, however, one area where I ran into some problems - exporting and importing my blog from wordpress into Posterous.

Posterous has a tool for importing wordpress export files and it mostly works without trouble.  However, there is one caveat - the file can't be too big.  I'm not sure size in terms of Megabytes is the issue but rather size in terms of post count.  I am not sure what the max size is that will work without fail but if your import fails in anyway try to re-export into smaller time period chunks.

For instance my blog has been around since April of 2003.  During that time I've written about 1300 blog posts.  Needless to say the importer couldn't handle that much.

I tried to cut the export down into year increments with the exception of my first one, Apr 03 - Aug 05 but it failed as well.  It actually looked like it was going to work but it got stuck on the 252 post.

On other imports, such as my Nov 08 - Mar 09 section (I had cut down to half year increments at this point) the upload portion of the import would fail.  In the status bar of my browser the upload would get to about 87% and then just hang there.  For other larger post count periods the upload would complete but the next page would never load and I'd get a timeout error.

I'm missing some posts in the move (less than 100).  However, the interface for browsing my posts in the admin panel on Posterous kind of falls apart when you have as many as I do so it isn't worth the effort for me to discover which ones are missing.

Another thing to note - Posterous says they will send you an email when the import is complete.  That isn't true.  I ended up doing around 20 different import files and I didn't receive a single email.

Finally, there is no collision detection.  That means if you import the same set of posts more than once - you'll get duplicate posts after you merge the imports into your blog.  Thus it is in your best interest to make sure you don't overlap your export files.

If you screw up just create a new space and make that new space your primary - then you can delete the old space and start again.