I really dont think that it matters if you store it verticle or horizontal unless you plan on archiving it. A while back I made a post about the whole storing dvd's verticle thing was a throwback from the vhs days. With vhs tapes, storing the tape on it's side will infact damage the tape. the weight of the cassette will cause the edge of the tape to curl. If you had one of those expensive vcr's that could put index marks on the tape (so it could automatically find any of several certain places on the tape), the index marks were the first to go if you stored it on it's side. the next to go would be half of your hifi stereo audio. After time the tape would curl enough to damage the video too (particularlly since the audio and the edge of the video were stored on the same space (the first layered recording so to speak). So I though that the crap about storing disks a certain was was a throw back from the vhs days. The only ration responce that I remember (it was on this forum so if I forgot something please forgive me), was that moisture is more liklly to collect if the disk is stored flat, so it should be stored verticle. So I asked, how can moisture harm a pollycarbonite disk??? The answer is mold!!!!! If micro water dropletts are allowed to stand on the surface of the disk, mold might form. I might think that this was bullshit but I know from my knoledge of camera equipment (and my famillys knoledge, which is much more vast than mine), A 2000$ camera lens can easilly have it's very expensive and very protectively coated lenses complettly destroyed by small traces of mold!!! The surface of a dvd or a cd is an optical surface just like a lens and mold can damage pollycarbonite, just like any other plastic!!!! This reason made sence so I bought it. Problem is, if you live in Texas like me, verticel or horizintal, your still fucked!!! Humidity destroys everything here (I know its not on the level of a rain forest but I'm from a colder climate (and its not just the heat, its the humidity!!!!! So it sucks!!!
I don't imagine that was the response you expected, but that was the only one I have heard that made sence. Franklly, if you are using the dvd's, it is probably not a problem. If you have or are trying to grow a library (even a tiny one like mine) where disk might sit for a long time unused, consider problems.
I know that people will say, by the time they could even mold, dvd will be obsolete (not true, it can mold in a month in poor storage (at least a camera lens can). It doesn't mater how long they last, by the time the disk become unreadable, dvd will be dead and you can convert it all to blu-ray!!!!!
I really bought into that who cares how long it lasts, It will last longer than the format will crap for a whlie. I now think diffrent. How many of you have transcoded dvd to hdtv (how long will that take to transcode)???? I just stopped myself from rambling on (a few more pages).
How do I store my dvd's? I dont think it matters. Pollycarbonite is not like glass (it wont flow over the years). I live in a misrable, humid climate (I know that their is worse), but my dvd's are in my house that benifits from the drying effects of of good old cold A/C year round!!!! The only place we have mold problems is in the bathrooms where thier is constant water.