The thing that bothers me most about OCs is that whenever I try to find fanfiction of a pairing I have to dig through pages and pages of characterxOC before I find something related to the pairing I was looking for (I've noticed this on FF.net especially). People, your OCs probably suck. Not all but MOST OCs are awful. If you want to create OCs and pair them up, try writing your own stories. You might enjoy writing original material more because you, as the original creator, can control EVERYTHING in the story. You can decide character personalities, what the universe they live in is like, what time period they live in, who the villains are, etc.
*Canada voice* Okay, my rant is done. Don't kill me.
'Write their own story' as in instead of canon charaxOC, write the same story but with OCxOC. An example (kinda) would be 50 Shades of Grey. I don't know how true this is, but it supposedly started off as a piece of fanfiction, but the characters were changed so that the story could be published. Just tweak the canon chara a little (change their appearance and parts of their personality you don't like), change their name, put them with an OC, and boom, original (to others, anyway) character.
Or just write an OCxCharacter fanfic and keep it to yourself, you could always do that.