I don't know how Bloomthat works, but I'm a little suspicious of anything that offers pre-arranged bouquets without any consideration to which flowers are in season. San Franciscans who like flowers might like http://farmgirlflowers.com/ : locally farmed flowers with beautiful arrangements and home delivery.

(Disclaimer: I have no connection to Farmgirl beyond being a happy customer. I feel like every time I carry my bouquet home I end up gaining them another customer though because people always ask me where I found such nice flowers!)