Not sure if its anything you can control but I've spotted that any image over the wordpress import size limit (not entirely sure what that is) fails. Luckily for me in a blog with over 500 posts only 30 of them fall into this category, just wondering if it can be avoided.
I'm in the annoying position of having to import images at 1040px width, just 16px over the 'large' size, so I have to go for the full size images. What would be great in a future release is if you could implement an automatic resize on import to a custom width. There's plugins that do this for uploaded images, im sure the flickr API works differently but it would save a lot of heartache (and bandwidth!)
Thanks again for a great plugin!