IMHO - acronym for In My Humble Opinion.
This is often used on online forums to indicate that the writer is aware that they are expressing a debatable view. Though in my experience it often is used as "this is the way I interpret it and as far as I'm concerned is a fact". I do not mind people using IMO/IMHO but don't use it as if it were evidence to support your claim.
I browse quite a few forums on several different topics. I have been on more than a dozen Ranma forums (not all in English), Buffy the Vampire Slayer, Slayers, Star Trek, consumer, environmental, political, religious, travel, comic books, anime general, manga fanscans, books, etc. I do not check any forum daily, I don't even go on the internet everyday, sometimes it will be weeks between checking them.
I am not, IMO, that active on any forum. I do not have 1000 post on any of the forums I currently browse. Some of them I have been browsing for a very long time, one forum, in which I used to trade fan subs via the postal service, I've been on for over 8 years. Even though I've been on that forum for so very long, I only have a couple hundred posts on it.
To get back on topic; I've noticed that a lot of what people think of as being facts/only possible interpretation are not in actuality facts. They are conjectures, assumptions, or one of many possible interpretations. If people use IMO while describing their interpretation, I have no complaint. The thing is so many people will than use that as if it were a fact even after using IMO which means that they already conceded that it is just their interpretation and others may have different views.