These come to writers in the form of crits. They can be awesome. They can be dreadful. When you receive these opinions, ponder the good ones, toss out the nasty, unkind remarks. I've had a few of those. One told me a way I could write my novel over again to make it work. Now folks, that one went the way of the delete button. There were some other things she said, but I have pushed them out of my memory. The good ones are constructive, gonna help you make your story better, crits.
Oath. This is a pledge you take. Lenny Lee has one. :-) It is a good thing to pledge to write everyday and to give crits that help, not hurt. (You also haz to take one when you stand before a judge.) *shiver*
Obnoxious. The people who give mean spirited opinions come under this category. *grumble*
Observation. Writers watch other folks all the time. They look at the way people hold their heads while talking and they watch their body language. Then they add it to their books. (They also enjoy listening in on folks conversations.) Purely for study, I assure you. *wink*
Obsolete. The typewriter. *exhales*
office. Where I write my best selling masterpieces. (Of course, even the first thing I ever wrote is a masterpiece.) I'z just waitin' on the right editor who understands my genius. :-)