How are 连绵词 used in modern Chinese?
聯綿詞 


聯綿詞 is a terminology in Chinese phonology. They are still functional 詞(compound words). 


  do they convey a poetic or archaic connotation?


Some 聯綿詞 adjective and verb do sound poetic or archaic (e.g 玲瓏, 翩翩, 叮嚀,  拮据). 

Some 聯綿詞 adjective and verb had become common day-to-day words (e.g. 荒唐, 嘮叨, 累贅, 凌厲)

Almost all 聯綿詞 noun are common day-to-day words (e.g. 琵琶, 橄欖, 鞦韆, 蝴蝶)