We’ve now turned on the ability for WordPress.com to import files from Livejournal’s export format due to a recent spike in requests. All you have to do is download your XML export and upload it to WordPress.com under the Import menu item, and it’ll import your posts and comments. Some features don’t map exactly, such as lj-cut, but we do our best to make the import as seamless as possible.
As always, if you run into any problems let us know through the feedback feature and we’ll take a look at it.
As a sidenote, the WordPress XML import/export that has been put into the 2.1 core trunk is coming soonish, we just need to finish up the plugin for the current release of WordPress.org so you can actually do something useful with the file, or get an export from your current WP blog.