Nusa Lembongan occupies a comfortable middle ground between well-trafficked Bali and relatively untouched Nusa Penida. It's not as pretty as either of the other two islands, but it has a banquet of good places to stay, a friendly bunch of locals and makes for a comfortable "time-out".
Lembongan is known for two things: seaweed and surf. Seaweed cultivation and harvesting is what keeps the bulk of the local population busy. It is farmed off many of the beaches (likewise on neighbouring Nusa Penida). Carrageenans are extracted from the seaweed, which are used for their gelling properties and as stabilising agents in cosmetics and foods.
Lembongan also has a number of very good surf breaks which attract a steady crowd of surfing enthusiasts, both to Lembongan as a destination in its own right, and as a substitute for Bali's more crowded waves.
Surfers and seeweeders aside, the island has a quaint village feel to it and there are some good (not great) beaches that haven't been given over to seaweed. There is some good snorkelling and you can cycle around both Lembongan and neighbouring Nusa Ceningan.
Other popular activities include snorkelling and diving trips around Lembongan, and, more often than not, to Nusa Penida. You can also do fishing trips, parasailing and other typical watersports. Surf boards (of varying quality) can be hired.
Part of the attraction of Lembongan is whiling away an afternoon, watching the seaweed undertakings and enjoying the sunset. Lembongan gets some great sunsets and can be especially photogenic.
It is well touristed and, unlike Penida, gets daytrippers by the veritable boatload, with Bounty and Island Explorer in Bali running offshore pontoons where their boats moor then disgorge hundreds of passengers to snorkel and visit the associated resorts on dry land -- sort of like a mini cruise industry.
Nusa Lembongan has two main villages, Lembongan village to the south, which is the main centre, and Jungut Batu village to the north. Most of the hotels and the main boat landing points are at Jungut Batu.
There are no ATMs on Nusa Lembongan. There is a single BRI ATM on Nusa Penida, but it doesn't accept Visa and BRI ATMs can be pretty whacky at the best of times. The waterfront of the main port has a few money exchanges and their signage indicates they can do advances on Mastercard and Visa as well. Some resorts will accept payment by credit card, but the majority do not.
Internet is becoming more popular with a growing number of cafes and restaurants offering WiFi either for free or for a charge. There are also a few internet cafes scattered about. 3G coverage is patchy at best. Blueline has WiFi coverage over the main parts of the island and coupons can be purchased costing 110,000 rupiah for 50 meg -- not cheap!
A small chemist on the main road stocks basic medications. The attendant is, umm, overly friendly and is obsessed with talking about kangaroo pouches. For anything more than a severe hangover, head to Bali.