I have wanted to go to this shop for the longest time and today I did. It's a cute shop, like the other reviewers have said. The yarns they carry a very excellent, and the staff is knowledgeable. But because the shop is so small the selection is limited, and what they do carry tends to be pricey. If you are looking for a wide selection of yarns, books, tools and accessories your best bet would be to go to Romni Wools on Queen Street.
I did end up purchasing some yarn at Lettuce Knit, but it was only a small number of skeins as I couldn't bear to spend a lot.
Lovely shop, very high-end yarns, limited selection.