A couple of years ago, I would have rated this place as a "must see", even if it was just to go there to taste all the different foods that this place produces (basically, anything that they can make from natural produce). Unfortunately, they appear to have reduced the size of the shop, thereby reducing the different type of produce to taste. Paradoxically, this may have happened because the business has expanded to include a shop in St. Ives.
If you are in the area, it is worth dropping in, especially if you are interested in herbs and the like.
Updated 23/05/11 - Farm now closed, shop still open in St Ives but owned by different people - no real change to the quality but has lost some of its charm. I suppose things change but why is always the best things?