Anyone been to Fiji?

I'm leaving for Fiji on the 16th, and we'll be there for 17 days. We've booked the first week at the luxury Cousteau resort on Savusavu, but we have 11 days left to do whatever. We have a flight over to Taveuni, but other than that we're free.

We're taking backpacks, so we'll be mobile. We're thinking of visiting Suva and Lekuva, then overland to Nadi and the Mamanucas.

Anyone have any experience there. Ideas of good places to stay, to eat, must sees, islands that have great beaches....