So there's an official statement about [Send to Kindle - Customer Service - O'Reilly Media](http://shop.oreilly.com/category/cust...), but I emailed amazon and got this (shortened) response:
Due to some technical glitch, our technical team has removed this feature temporarily and they are working on this to rectify the issue.
On high priority, I've forwarded your comments to our Kindle technical team, so that they can look into this and with great regret I've to inform you that the feature of Send to kindle is taken for review and consideration.
I'm sorry to inform that the API for this has not yet implemented and I assure you that this feature will be made available soon.
I'm starting this thread just to keep tabs on the progress of this feature, as I miss it sorely. Having to use the Send To Kindle software is a pain and requires me to download the mobi just to upload it back to amazon, which is sometimes not possible for larger files when I'm on a data/bad connection :-/
(I did discover, though, that when you delete the Author in the Send To Kindle software, it's smart enough to pull it from the mobi, which was not at all obvious).