I had lunch here in 2007 and remember it now seven years later as one of the best lunches I had in the two weeks I was in Paris.
When you enter you are greeted and seated at very tasteful, cloth covered and somewhat tight seating arrangement. The French carry on in soft conversation, many people make a quick glance as plates of food go by.
The food is infused with various Mariage Freres teas; sometimes a tea infused sauce, sometimes with tea in the oil, and sometimes with the flower petals declicately tossed over the top of the chocolate pastry. It's beyond decadent, and elegant! If you are intrigued and research this salon more, you'll see many people comment about the service. It's impeccable. It is a meal that you eat slowly, it is food and atmosphere that is really intended to be savored.
(*I would recommend "dressing for the occasion." You'll see the local's wear skirts, slacks and jackets in the summer. Remember that in Paris a scarf will make any attire more chic.)
If you are not able to dine, then do at least visit the shop, which is also at this location facing the street. The dark wood paneled walls support giant antique metal tea casks. Some of the staff are bi-lingual and multi-lingual and are completely kind and professional answering questions and giving direction about which tea to buy. You can smell and sample the teas as well as shop for the accessories like scoopes, infusers, and bone China.
If you love tea, make the pilgrimage to Mariage Freres!