Absolutely. Really quiet, under-developed and with some of the most beautiful beaches I've seen in years.
Best to take a ferry and they probably have a set-up with a tour company.
We took the coach trip, which dropped us at the beach for 3 hours and then took us on a whistle stop tour of the island. At the bottom of the island, there are huge hills and cliffs, from which you can see the whole island (really flat) and Ibiza in the background.
It took 3 visits for us to visit, but it was well worth the trip and the money.
It took you 3 visits, it took me 7 trips to Ibiza to finally get off my arse and get to Formentera.
It is definitely worth it tho, you might think it is a bit of a hassle getting a boat from Ibiza Town etc etc but it is so chilled and peaceful, you come back feeling like a new woman (or man)
That said I never managed to get over there again in June even tho we were there for 2wks. We're going back tomorrow for a wk and I can't see me getting myself sorted to get over there when I've only got 7 days so I'm going to have to wait til next year. But really make sure you make the effort and go, it is so worth it.
We just got the fast-boat from Ibiza Town and then just spent the day over there doing our own thing, found a fantastic beach and a lovely restuarant.