For all those saying that you cannot take an AOO during the surprise round with Combat Reflexes because you are unable to act, consider that an AOO is not, in fact, an action. It's not a standard, full round, partial, swift, free, or immediate action... it's just something that a character can do under certain circumstances defined in the rules, with a certain frequency (normally, once per round, only when threatening an enemy who provokes, and simultaneously not flat-footed). Actions are defined game terms. It seems reasonable to me that "unable to act" most literally means, "unable to take actions" since that is the game term that most closely matches the terminology used. AOOs are very well fleshed out in the rules, and are most certainly not actions... so, if all the conditions for using an AOO are met, I see no reason why one could not be taken.
Venator earlier broke surprise down as follows:
1) Unaware characters can not act.
2) Because they have yet to act in combat, they are flat footed.
I would break it down a bit differently.
1. Surprised characters have no initiative count (because they are not entitled to roll yet)
2. Surprised characters may not take actions (really a side effect of not having an initiative count, although it is specifically stated)
3. Surprised characters are flat-footed (really a side effect of not having acted yet, although it is specifically stated)
In addressing those restrictions, I would say...
1. Nothing in the rules for AoOs requires a character to have an initiative count to take an AOO.
2. AOOs are not actions.
So, for most characters, only #3 is a problem. However,
3. Combat Reflexes allows a character to make AOOs while flat-footed
I do believe it was the intent of the writers for Combat Relflexes to enable AOOs during a surprise round. I also believe it is of reasonable power level for the feat. I further believe that the specific way in which the relevant rules are written support this position.
That said, I can see that it is not written with perfect clarity. The above is just my best effort at interpretation of what was written and intended in the PHB. If an errata release or faq answer were to say that AOOs could not be taken, even with Combat Reflexes, then I would go along with it.