This will not affect many people here, but if it helps just one, then it's worthwhile to post it.
If you have been married abroad to a Brit for 4+ years, and the Brit has been engaged in Crown Service, you can apply for permanent residence (ILE) at a post abroad WITHOUT taking the KOL. In place of a KOL certificate, they will accept a letter of reference from another Brit which confirms that you have sufficient knowledge of life in the UK, and do not need to take the test.
I thought this was too dodgy a loophole to be real, but it's been confirmed by an on-the-ground case. As I said, few people will actually qualify, but it's worth knowing anyway...