I am by no means a professional brewer but I've made a half dozen fruit/spice beers and I have gleened a little insight from it. Aging a beer on whole fruit can add a nice zip to an otherwise nice beer. If your beer isn't any good to start with don't waste your money on fruit.
The first fruit beer I made is a beer I made with Derek when visiting him in the early summer, there was still a chill in the air(which persisted into july this year), so we made a chocolate porter. We spiced it up with raspberries, and vanilla beans, and chocolate. Mistakes were surely made: the seeds from the raspberries made it into the beer as well as raspberry floaties. In my blackberry pale ale I limited most of the floaties but there are still a few, it's sad, but at least there are no seeds.
What I needed to solve the problem of seeds and the problem of floaties was a syphon filter. My solution to this was to make a very narrow bag for my my syphon. This worked brilliantly both times that I have used it thus far. It took no sewing acumen to craft. I barely used maybe 8 stitches along the length of the bag and a running stitch along the bottom. In the top picture you can see the sleeve. It fits the length of the syphon and is held up by being tight. It also stretches out from the top of the carboy and the tightness prevents it from slipping in. The stitch in the bottom picture is just putting the needle through and making a knot 2-3 times. then I would run the thread for an inch and make a few more knots. You could cut the thread each time but I find that unnecessary. After it is stitched turning the bag inside out will put the seem on the inside. This prevents getting crap stuck in the stitching. The porus material I used is the same material I used for my 'brew in a bag' bag.
So with the sleeve in hand I set about bottling my Belgian Quad aged on tart cherries and my Ginger Rye Munich Saison aged on fresh ginger. Both beers had tons of stuff floating around in them, ginger shavings and cherries. For whatever reason some cherries floated and some sank, and most of the ginger sank. you can see the ginger saison mid siphon(right) with clear beer in the syphon tube and the syphon resting on the ginger, a picture of the clear Belgian Quad(left) and the leftover cherries(right) which I syphoned the majority of the beer from.