used eDead v3 - the liquid type. worked very well for me. I did the whole trunk, under the rear deck, the trunk lid, and behind the license plate, and a little bit of the inside of the bumper (that you can see from laying under the car...lol).
the first good thing was that was easy to put on. just paint it right on and make sure you can control the droppage when doing stuff upside down.
the main difference was that before I eDead'd the trunk, and I open the trunk up with the system playing, all you heard was just 60% bass and 40% rattling/noise. of course from the inside of the car though, I'd hear all bass and no rattling...but once I open the trunk it got pretty nasty. so after I deadened it, I absentmindedly realized how the only "noise" I heard was only from the fins of the air vents in the trunk. and that was it...I think I opened up the trunk to grab something out of it, sat back in the car, and then "just" realized it.
the second main difference was that I got a huge increase in the lower midbass range....around 75-90hz. this made up for the poor midbass I got from kick panels...which is the primary problem...but setting my bass crossover around 90hz at least fills the gap.
the third thing was that noise that occurs outside the vehicle, e.g. rattling of the trunk lid, license plate, etc., was reduced significantly. however let me add that in addition to eDead, I used some expanding foam in the holes of the trunk lid & primarily behind the license plate. without that foam behind the license plate, I'd still have rattles (with just 1 layer of eDead behind it).
well, as far as bad stuff, I don't know if you consider it bad or not, but basically the deadener keeps inside sounds inside, and outside sounds outside. cause sometimes I'll be rolling down the street with all windows up & the system going, and from the outside, you pratically hear no bass. the only sounds you could hear are those areas which need more sound deadening techniques applied.
also, after I deadened the trunk, there is a noticeable "outside" increase of midbass with the trunk open, and an increase in sub-bass inside the car with the trunk closed. before, it would be the same. this may just be an artifact of my car or whatever, but just thought I'd mention it. the way I think about it is
my trunk before deadening = a cardboard box
my trunk after deadening = a brick wall