Table 9-6 p. 147 mentions the modifiers for a character "Kneeling or sitting" but there aren't any other reference to these "conditions" (unless I missed them).
What type of action is required to "Kneel" and Get back up, I would assume a Move Action, does it case an AoO? I would think not. What type of movement is allowed while kneeling? I called it at allowing only 5' steps (no AoO).
On a personal note, I allowed characters Kneeling to use a Heavy Shield to get full-cover (as a Tower-Shield) as a Standard Action.
Anyway clarifications would be usefull.