Thought it would be worth mentioning a warning about what may happen to the unaware traveller when you land in gilli air harbour off your ferry or fast boat. We landed without booking any accommodation. This is not unusual, we thought we would find it once we arrived. Unfortunately on disembarking we got distracted by a local who said he had decent accommodation so we ended up walking with him to the centre of the island, rather than to the beach/shop/restaurant area. When you arrive in the harbour you cannot see the main shop/ beach area. By taking us to the centre of the island we ended up in quite dull accommodation, far from the main part of Gili Air and in accommodation which we could have paid (and did the next two nights) the same price for much more modern, clean and conveniently located accomodation closer to the main beach and restaurant area.
Gili air is lovely, it has a more sophisticated air (pardon to pun!) than gili trawangan, and also has great snorkelling. The beach can have a strong current, so it can be quite an effort to snorkel for an hour or so, but many, many fish to be seen.