Caliban said:
...I think that in order for a free action to provoke, it would specifically state it. Otherwise it's a typical free action....
Almost by definition a move action turned into a free action with a feat is not "typical," right?
I think that you'd still provoke an AoO unless the feat specifically said otherwise.
Of course, a DM is always free to rule either way, but my expectation in a new group (not knowing the DM) would be that it would provoke an AoO.
I see it going something like this:
"Hi, I'm new."
....
"I stand up instantly without provoking an AoO."
DM: "How do you do that?"
"I have a feat"
DM: "Does it say you do no provoke an AoO?"
"Well, no, but it does say standing up become a free actaion, and free actions usually do not provoke AoS, right?"
DM: "Sorry, the BBG swings at you with his AoO..."
Hmmm.... that bit about a free action usually not provoking an AoO and therefore none is provoked in this case seems a bit... lame, doesn't it? At least it does to me. Generally speaking, rules that are changed by a feat must be quite explicit or one should assumed the rule was not changed.
The rule is that standing up from prone is a move action that provokes an AoO.
The feat changes it to a free action. No mention is made of the AoO.
Free actions
usually don't provoke AoOs. This, on its face, seems to be an unusual circumstance where a free action provokes an AoO because it's a move action chaged to a free action without removing the fact that it provokes an AoO.
Maybe I'm wrong, but it sure seems straightforward to me.
EDIT: As for using two move actions (prone-knell, then kneel-stand) to avoid an AoO, that's up to each DM as no actual specific rule exists for this. I'd tend to think that prone to any other postion provokes an AoO, but not from kneeling or sitting to standing, but that's just my opinion based on other AoO rules and the general description of an AoO.