Put 5 lbs frozen cherries in a pot and fill/cover with water. Bring to a boil for 10 min. Purée in blender for 5 seconds. Cool to pitching temp in the freezer. Put straining bag in a small container and pour in cherry purée and juice. Rack beer onto both straining bag and juice in secondary. This method is intended for 5 gal batches.
I have brewed both cherry wheats and raspberry wheats with this method that gives good, not overbearing results. The flavor is there, but doesn't taste artificial like Sam Adams Cherry Wheat. The raspberry tastes awesome but the flavor will start to dissipate after just a month or two. The only problem with doing this is the price of frozen fruits, five or six pounds will run you $25 or more. Hope this helps, cheers!