Hello there, my name is Jose, i was born in Menorca and have lived in Calan Porter for a long time, but have spend lots of winters in London.
Anyway, in response to your question about if there is any nightlife in Menorca in August, the clear answer is YES. To every other one who has been here in holidays and says that there is no night life, is because they have'nt look properly.
As a local, and being young, 28, im a bit fed up with the old topic of Menorca is an island for families and for older people. There is in fact lots of families, and old people, but i can tell you for a fact that there are lots and lots of bars, pubs and clubs, you only need to know where you are going to find them. Calan porter for example has one of the best clubs in Europe, called Cova den Xoroi,
http://www.covadenxoroi.com with different nights like Urban Flava on Tuesdays, Freeestyle on wednesdays, Foam party on thursdays, Ibizaabla every 2 weeks, Playhouse every two weeks, Italian Dolce vita every monday.
The problem is that the people that normally writes reports in this sort of holiday report websites has never ever been out to them nights !!! Calan porter has a great night bar-pub-club, called Flava Bar, with pool tables, live dj, cocktails, shots, its pack everynight of the summer but again you wont find anyone that has been there writing reports in this websites.
Seriously, there is plenty of bars and pubs and clubs in Menorca, and all we need is a few more people on their 20's to come and find out the truth, and get rid of that old topic of family island.
Anyway, also check
http://www.urbanflavamenorca.com and if you need to know anything else let me know.
Jose.