Use may be regional. In my native Los Angeles, "affectatious" was in regular (well... not infrequent) use, unlike "affected", which can cause confusion. In the UK, I have heard the latter, but not the former. Likewise, there are many words used regularly in the UK that have fallen out of modern use in much of the US.

On a separate note regarding language evolution, I'm forcing myself to write "use", rather than "usage" which has become acceptable professional jargon in my field.