This question came up when I was playing against a Grey Knight player and intended to assault a squad in which was a librarian, who knew the sunburst psychic power.
As an overwatch reaction is says that unit firs as per a normal shooting phase, so can he use sunburst in his overwatch? In fact, as a more generalised question, can you use a psychic shooting attack (as long as it isn't a blast) in overwatch?
Okay so, the way I read it, is pg69, says Witchfire powers are treated as psychic shooting attacks and are manifested in the shooting phase, and overwatch is treated as a normal shooting attack, albeit resolved in the assault phase. So, I don't think witchfire can be used.
But what about nova attacks? They don't target a model/unit but are still shooting attacks, so they are more of a grey area.
If it does work, does this mean, an Eldar Farseer could use mind war against a charging unit, sniping out one of the members of the unit? Because that would make charging a farseer slightly more risky!
Also, warp charge tokens, dos this mean a mastery level 2, can only use 2 psychic powers in both his, and the opponents set of phases? I'm pretty sure I'm reading it right anyway.

There is a lovely bit of wording on page xvi that says:
...in each turn, both players move, shoot and fight with all their warriors. Each players turn follow a specific pattern...
So in that one sentence they have given two different meaning of the term "turn".
And page 66 says:
A psyker generates his full allocation of Warp Charge points at the start of each turn.p
Do we follow the old tradition of unless it says game turn, it means player turn, or do we go with "accept first answer" from the rulebook saying that a turn is both player turns? It's lovely and clear...
Also, fun bit of trivia, pg69 top paragraph, at least in my copy has "are" spelt "aer".

Cheers,
- Will