We recently upgraded WP to 3.5.1.
Our install is sub-domain multisite.
Since the upgrade import successfully imports the first item (post) and fails on all other items: Tags, Categories and further articles.
I tried modifying the import.xml to see if I could isolate what is causing the failed import.
The only way I was able to successfully import is changing the status to "published". However, as I am sure you are aware this results in the posts not displaying in Admin or on Front end. I then modified the db entries to "publish" and everything looks great.
I was able to repeat the above many times. All other modifications I tried gave the same result of nothing importing.
I would love to see this fixed as I use it regularly.