The atmosphere is relaxing, the coffee and tea are delicious and the prices are incredible. The service is pretty poor and I can echo the other comments about the sandwiches being cut off at an unreasonably early hour. Some times, they run out of the ingredients to make the sandwiches before noon on Saturday.
Don't let the sign about credit cards not working fool you. This place doesn't take credit cards.
The free WiFi works about 10% of the time, possibly less. If you need to get something done, don't chance it here.
In short, if you want a cup of coffee or tea and no frills and you brought cash, this is your place. If you're expecting anything else (like a sandwich or the internet) commonly associated with a coffee shop, keep going.