Security 007:
You can't assume that an aircraft is inherently nose or tail heavy just by looking at its outward physical appearance or seating configuration. The aircraft's loading (and the resulting COG location) is carefully calculated before each flight.
On any given flight, an aircraft may be slightly nose or tail heavy in relation to its "standard" CG, but it a regulatory requirement that the loaded COG must fall within well-defined limits that would prevent any situation where excessive control surface deflection or trim inputs would be required to keep the aircraft flying level.
That's not to say that mistakes don't happen. Several years ago, a DC-8 freighter crashed on takeoff in Miami because an improperly-secured load broke loose and slid aft when the nose was raised, causing a loss of control.
Crashes due to out-of-limit CG conditions are (unfortunately) not uncommon in small, privately owned aircraft, but very rare in commercial operations.
It would be incorrect to say that the Q400 is by its nature a "nose heavy" aircraft. If it were, it would never have been certified.
At the latest NTSB press conference, they said the the FDR data shows no unusual trim inputs were being commanded by the autopilot, which would tend to rule out CG issues as a contributing factor.
In any case, I'm sure that the NTSB will look closely at the calculated loading for this particular flight - fuel, passengers and baggage.
JRBarrett