Update
I've finished getting all of the QUOTE tags working properly now. That's basically it for the BBC stuff*. I can't think of any more that need work right now. If you notice something wrong with a BBC tag, or notice one that doesn't parse anymore, let me know.
To explain more, we now have old quote tags (that use legacy post IDs) working and linking to their proper thread and post. New quote tags are created with the new post IDs, and those link properly too. Some users have spaces in their names, so they need quotation marks around them to work properly, and those are now added automatically when quoting a user with spaces in their name. So yah, it's all working now.
I believe I got the correct icon we used to have to link from a quote to the post it came from:
See 4 posts above (#185) for many styles of quotes working (and especially linking) properly now.
*Edit: Actually, I forgot the SPOILER tags. I'll get them working some time soonish. Oh, and ordered list don't work yet (unordered lists do work).