Before saying this is a report, I can certainly tell you that it is not. I have known this for a long time and have been doing it for a long time so today I am going to share it with you.
There are two ways to keep any or all raid buffs.
The first method is) Join a large common battleground with several players (AV/EoTS/IoC) and get all the raid buffs. Upon doing so, type /afk. When you afk out, you will keep all buffs.
The second method is) After completing a raid, inform the raid leader kick you from the group after you log out. Once you log back in, you will have all the raid buffs still.
This is not a repost and if you say that it is, do provide a link. Additionally, I noticed that someone had posted something about keeping blessing of might or whatever paladin buff and though I was originally planning on adding this information to his/her topic, I felt it was more appropriate to just create a new topic with more details and information on it.
Later