What are some good methods for long term water preservation?
Things like stockpiling water...storage issues etc.

As many big ass water containers as you can store (i.e 55 gallon drums or 7 gallon aqua-tainers) and the appropriate amount of unscented bleach / gallon of water.

I personally use the 7 gallon aqua-tainers because they are easier to move around and store. Every 6 months I empty them all, clean them well and then refill them and add bleach.

I also keep (10) 30 packs of 16 oz bottles of water on hand. Easier to use in short term situations.

how long are the packs of 16 oz bottles good for? roughly?

I rotate through my stock so that I never have a case for more than about 3 or 4 months. I wouldn't hesitate to drink the water up until about 1 year though - AS LONG AS IT WAS STORED CORRECTLY. If you keep them in a cool, dry, dark place (think basement closet) where the the temp is pretty constant - they will be GTG for quite a while.

My whole philosophy on preps (and I'm a rookie compared to most on this site) is to keep a solid month  to 6 weeks of REGULAR food and water for myself, my wife and 2 kids. I rotate through all of it constantly - I use my preps as the "grocery store" and then replenish the preps on my next trip to the "real grocery store" (Hope that makes sense). Therefore, I never have anything around for more than a few months. I'm currently looking into getting some more long term preps that I probably won't use (grains, beans, etc) and try to get myself up to maybe 5 or 6 months of food. I'm fortunate to be in an area where I can hunt/fish to add to my food supplies, if need be. I also have a ton of water around me and the means to collect and purify it so I would be good there as well. My preps (to me) are basically to make the initial event as easy as possible without having to worry about food and water immediately.

What happens to water after being stored a long time? I would guess it would go stale but would pouring it back and forth between containers several times oxygenate it? Then run it througn a filter maybe?

My understanding is that unopened bottles of water can be stored indefinitely. I would guess they would get stale as you state but I don't think there would be any need for using a water filter on them if they were stored and never opened.

The reason I use the 7 gallon aqua-tainers is that it's cheaper. I bought the containers at wal-mart for somewhere around 8 or 9 dollars. Admittedly they are more of a hassle because you have to treat the water but - the cost savings is worth the hassle (to me) for the money savings. Plus, if something big ever did happen, I would have a bunch of handy containers to tote water back from my local stream.