My experience :
I made a raspberry wheat (5gal) and used 1 can of raspberry puree (vintners harvest, 3 lb) in secondary. It was a DRY beer and it turned out VERY acidic. It was good, but very very tart and dry. NOT a sweet girly dessert drink by any stretch.
I bottled a simple pale ale with blueberry extract last month. I used 2 oz of extract in the bottling bucket. This beer was sorta based off of a seadog bluepaw clone. The blueberry flavor is perfect in terms of strength. I think it tastes....artificial, sort of sharp. Almost medicinal. In the future I will try using both in combination to see if it's better balanced (and because I want my blueberry beer to be blue dammit!)