Once, I was showing somebody my book, and when I told him it was set in medieval times, he up and quoted a verse in old English. It was interesting.  
 
 Svensteel priest of kylor wrote:
Asking people about the different voices and styles of their writings, in the way of newer to older vocabulary words. Do you use thy? Forsooth? Alas? And surely you wouldn't use things such as, gnarly, bodacious, and rocking? Though I sometimes use newer words in dialogue of fantasy in exocosmic books, but not ever in the actual writing of the book. Do y'all?
I use no thees, and nary a thy wilt thou find in my writing. (Hee hee! I couldn't resist...  

 )
Really old words I use rarely, if ever, and even then they are usually in formal speech.  I do, however, use plenty of words which are not common today.
Such as: “That fellow yonder"  or “I daresay he will" or “Is there aught I can do?” I have a question. Does anyone ever use a 'colloquial' speech for some of their characters? Here is a sample of something that I use.
Quote:
“That’s all right,” Jausten assured him. “I know a yen a’ th’ hill-speak in m’own head.”
Leed looked amazed to hear Jausten speak so, for he had never heard any of the low-landers bother with the easy manner of speech his own tongue preferred. “You do?” he said.
“Ya. I take it in m’ care to catch what a’ can av th’ customs a’ folks about. See, a’ve been ‘round a bit, an’ it comes as nature t’ me t’ blend wi’ others.”