When someone goes ahead and makes a post or thread with capital letters, I usually take it as SHOUTING or trying to get their point across quickly. However it depends on what they are saying.
For example, if one were to put in capital letters, THANK YOU or LOL DUH. It doesn't in actuality have to mean shouting. But if one were to put: I KNOW THAT. This short sentence shows a lot in meaning as shouting, rudeness or just trying to get a point across. I suppose only using capital letters for when it is needed is necessary such as in the beginning of a sentence or the letter 'I', is better for those who get offended by it in some way. O_o; Other than that, for myself, I use capital letters briefly and try not to get anyone offended.
...Or if someone's caps lock is stuck on, then...THEY WILL USE CAPITAL LETTERS ALL THE TIME. XD