Hey Gordie, and greetings from Petaluma.
I've been thinking about using these as well, especially after the success of a beer I made which included some lemon zest. I might consider doing something with lemongrass too. I'm hoping we're going to have weather like this all summer and I want to keep one or two lighter beers around.
I've read what people say about using the kaffir lime leaves and it seems like most people go with somewhere around 5 leaves for a five gallon batch. You might want to use more if you're hopping more heavily.