It should be obvious, but just fyi...
Anything posted here could cease being free with any update to the PSN Store.
Regarding "cross-buy" add-ons...
Sometimes you may get a message that says:
"You are not eligible to purchase or download this content."
This happens when you add a cross-buy item to your cart and then attempt to add the same item for another system to your cart. If this happens, just purchase/order one version, and both will be added to your PSN library.
Only ten things at a time...
You can only put ten items in your shopping cart at a time. If you want more, just check out. Once your purchase is complete and your cart is clear again, you can continue with additional items.
Don't own the game? No problem...
You don't have to own a game to add its DLC to your library. You can even download the add-ons for games you don't have yet.
RSS is your friend...
If you're not using an RSS reader yet (R.I.P. Google Reader), I'd highly recommend it (Feedly is a great one). It's basically an article listing that you populate from whichever source(s) you want. For example: Google News, Ars Technica, PlayStation Blog, your favorite subreddit, local news site... or this blog. If you add this URL to your RSS feed, you'll know every time an update is posted: http://psnstorefree.blogspot.com/
Thanks, Yechezkel, for your contributions to the community. =)
