RSS feeds are gone. I'm not sure what's wrong with the API, but portions of it appear to be broken.
It certainly breaks the bundle feature I was using to organize tags for the kink meme account. It has replaced bundles with tags named 'has:bundlename", which completely misunderstands the semantics of bundles. Every link now has "has:kink" has a tag, because every link had a "kink:foo" tag, and every "kink:foo" tag was in the "kink" bundle. Bundles were a way to group tags, that is, they were a trait of tags, not of links. That meaning has been entirely lost.
Now. Try browsing around on the kink meme account. Click on the "!prompt" and "!fill" tags. Notice that they don't work. Delicious fails to find any saved links with those tags, even though the tags are present in lists and you can see many, many links tagged that way. Why is this? It's because they're no longer escaping special characters in urls. See section 2.2 of RFC 3986 for the list. They are not escaping the bang. Also not escaping the colon, it seems, though that works. Inconsistent handling, I'm going to guess.
Holy crap they broke all tags with / in them even worse. Children, children, this is why we read RFCs and do things like use standard URI handling libraries, because the problems are boring and already solved.
This is merely a bug, albeit a staggering one. They'll fix it eventually. However, this particular bug reveals a certain base-level incompetence that disturbs me. Shoddy work. Insufficient testing. I think Pinboard is about to get some more of my business.
ETA: Bookmark import chugging on a shiny new Pinboard account.