The problem is that it isn't a set number like adding sugar because fruit also adds water. Because of this it effects different beers differently, in a low gravity beer fruit will raise the alcohol, but in a high gravity beer it will actually lower it because it adds a lower ratio of sugar to water than the base beer.
I don't mean to be cheeky, but does it really matter anyway? Just seems to be a very common question - and it's not like we need to label the bottles with the ABV!
It would generally be a small difference due either way to the increase in water that accompanies the fruit/sugar.
Thanks for all the info, especially the "sugar and acid" chart. No, it doesn't really matter to me what the ABV is - but I've got a girlfriend who counts calories so it helps keep me in good standing with her.