Two points in agreement with everyone:
2 actions are needed IMHO for the HMG gunner to disembark. This is due to the fact that he can shoot the weapon from the Orca. It is locked in, I assume, a mount on top of the Orca. It would take one action to undue these locks and one to disembark (normally) from the Orca.
As for the extra activation not being a major plus, I would have to respectfully dissagree. I don't try to min/max my armies, but it seems with more activations and alternate activations you have the ability to pick/choose your battles and hold back your stronger units to be at better/closer ranges with little or no return fire (at least that turn). Having three extra activations (using three Orcas usually in my armies) helps greatly to achieve this. Not to mention 3 HMG's wondering around helps alot also. They greatly protect the Orcas and surrounding units from enemies that are closing in. PB 3(x3) and SR 1(x2) with RC of 9 AR of 18 is nice.
Did I mention I love Orcas.
You can conceivably have 6 on the battle field with a 1000 pt army. Hmmm
To those that would get this - 8 ball in the corner pocket.