How does everybody handle this? It seems like the actual printed rules assume you aren't using a grid system, though this is still bound to come up from time to time surely? What is the general consensus about moving through enemies/allies, also what about hordes? What happens when a character finds himself 'inside' a horde so to speak, surrounded by foes?

Are you asking for a rule, or an opinion?

If it is the latter you need to ask it either in the general or gamemaster forums. This section if for questions concerning rules.

The rules do not specify what happens with a "grid-system" as it isn't required to use a grid system to play the game. You don't need miniatures or grids for roleplaying games.

Hordes can be walked through by marines.

Alex

_{I think it is assumed that even with hordes they aren't packed together like a phalanx but rather have a 'zone of control' (No that isn't explicitly stated in the rules). Hence I think Pcs and NPCs can move through hordes as necessary. of course if a PC insists on standing in the middle of a horde I might give the horde bonuses to hit.}

Well, I would add from a rules point of view:

Engaging a target does not require any form of action. If a marine advances into a Horde, the Horde can immediately engage the marine the moment he moves within melee range of the Horde.