the occlumency trainer harry hires is able to read deeply within harry's mind without a lot of trouble. I think thoughts are probably easier or harder to read based on how surface they are. Dumbledore made them think of something else so he wouldn't accidentally read anything private because of how EASY it is to read surface memories, not because thinking of something else prevents being read entirely.
There seem to be two forms of leglimency, one that requires an explicit spell and a wand, and can be performed by most wizards. That's what Mr. Best in MoR uses, and what canon!Snape uses while trying to each Harry Occlumency. The victim knows what's going on, but usually can't do anything against it.
The second one is the form that Dumbledore (and canon!Voldemort), which just requires looking into the eyes of the victim, and lots of training. This is the "stealth mode", and most victims don't notice the intrusion at all.
It was always my intuitive...
(The HPMOR discussion thread after this one is here.)
The previous thread is over the 500-comment threshold, so let's start a new Harry Potter and the Methods of Rationality discussion thread. This is the place to discuss Eliezer Yudkowsky's Harry Potter fanfic and anything related to it. The latest chapter as of 09/09/2011 is Ch. 77.
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: one, two, three, four, five, six, seven, eight. The fanfiction.net author page is the central location for information about updates and links to HPMOR-related goodies, and AdeleneDawner has kept an archive of Author's Notes.
As a reminder, it's often useful to start your comment by indicating which chapter you are commenting on.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: