I've never seen it before, and I am pretty sure we don't use it any more.

no, it's not traditional form, it's one of the variants, both forms (喫 and 吃) were used simultaneously in history, none is more traditional than other

喫 一般被當作 吃 的 異體字 喫 字消失在中國 而卻仍然活在 臺灣和日本 臺灣的飲料商品名稱 http://www.savesafe.com.tw/Products/ProductView.aspx?s_id=852e699dd293b4cbb9a3a35b62803288&t_s_id=12656 日本的喫茶店 http://ja.wikipedia.org/wiki/%E5%96%AB%E8%8C%B6%E5%BA%97 這個 喫 仍然留 "飲 /食 /吸" 的古義 但是 吃 在 形容 說話結巴、言語困難的樣子 如 "口吃 ji2" 或是 形容笑聲 時 如 "笑吃 ji2 吃 ji2不止" 這時 吃 並不等於 喫 這時的 吃 維持它的古義與古音 口吃 在臺灣 念成 口 ji2 另見 http://www.italki.com/question/209416

Yes,It is the traditional form of"吃"，and good for you to know it.I often feel sad that as Chinese ourselves have forgot the traditional way of writing traditional Chinese.Against most Chinese' oppinion,I advise you to learn traditional Chinese while working on simplified at the same time,especially if you study Chinese not only for business but for understanding Chinese culture.It is more representative of Chinese tradition and Chinese philosophy and ,it is used today,in Taiwan,Hongkong,The official written form is still traditional Chinese,which makes it meaningful even for pragmatic reasons.Hopefully my words here means something for you .Best wishes on your Chinese study.

"吃" is a verb not a quantifier.