I can confirm that the modified code does not work, which is a shame as URL sideloading would be awesome!

I've resolved the first issue, but with regard to the second issue, the fix_product_subcategory_query() function breaks the single template for my custom post type. Specifically, it just loads the generic "single.php" template and not the one for my CPT. Can you offer any resolution?

This code does seem to work but it causes a couple of issues when I implement it on my website. First, it causes Posts and Pages to break - only items under a custom post type actually work. Secondly, for some reason the code causes the single template for my custom post type to be ignored entirely. I've been trying to figure out the cause, but no joy yet!

Yes it goes without saying that the comment form will need to be added to author.php - this is covered in the answer I provided a link to.

Specifically, after creating the post type, how do you make it so that each time a user/author signs up, a post gets created in the custom post type and associated to their profile?

I know this is an old answer, but I was hoping you might be able to give some more detail about how to do this Bainternet?