I spent few days in Con Dao in October 2010, and although we had a fun week-end full of 'experiences', I might still say this is not the dream island you might think of to spend few days - especially if you are a backpacker and have the correspdoning budget!
First of all there is no transport from the airport, therefore your have to take a van of a hotel (i.e. that you are supposed to stay in the corresponding hotel). If you want to chose the hotel only once you arrive in Con Son city, then you should pay the driver of the hotel van to drive you there.
If the island attracted many tourists in 2006-2007, it seems most of the tourists now are Vietnamese, and the few hotels that you will find beside ATC, Con Dao resort, Six Sense are reserved for locals and forbidden to Vietnamese.
There are very few hotels on the island, and the prices are, for most of them, a rip-off, at least USD65 (promotion price). We had found some rooms in a guesthouse (in a family) but the police refused the authorisation for us to stay there.
SO we headed to the cheapest hotel, Phi Yen Hotel (300 000 dong/night/pax if i remember well), is the cheapest but in a quite terrible state, not maintained, dirty, falling apart...anyway, just consider this place to sleep and take a quick shower.
There is no pristine beach on the island itself, as far as we have seen, maybe on the islansd around.
The Con Dao national park has a new guesthouse, which was closed at the time fo our visit, and the rangers told us it was not opened to foreigners.
The dive centre, 'rainbow divers' has closed down and although it was supposed to open, is still not opened. However, on our way back to HCM, we met at the airport a young couple who should start a dive center in the coming months (early 2011) there...to be followed.
We enquired at the park for diving but the officer was not really aware of what was possible (I must however say it was not the diving season in Con dao).
We also did a 1-hour walk from the national park office to the opposite side of the island to an 'isolated' beach, where there is a bungalow and spartiat rooms, a beach of rocks and gravels, and waste...
There is one 'travel agent' (con dao travel agency), which hardly speaks english and is rather lousy.
We made a walk in the jungle (strating from the airport) with him to go to one of the supposedly best beach to snorkel, and throughout the jungle the guide did not explain anything about the flora (we did not see any animals), and was simply rushing forward, hardly waiting for us. We arrived at the beach (northern bay of the island, bamboo lagoon), where the national park office is building a new office, and where cement bags where piled up on the shore...what a disastrous view!
Even though the landscape can be nice it is simply spoilt by the developments going on. Moreover the wlak on the aiport beach after the high tide gives the impression to be walking in an open-air supermatket as all the waste from the fishermen are dragged to the shore with the tide, you can chose from flip-flops, hat, polystirene boxes, toothbrushes, bulbs, etc...
We however found a great restaurant where we ate delicious food for nothing, and i must say it made-up for our stay!!!!
In conclusion, unless you are a diver and wants to go diving there (and if some dive centre has opened), there is no point of going to Con Dao. We had a good and fun 4 days there, but there is nothing special in this place. It does not hurt to go there but it does not deserve a special trip.