Personally I'm of two minds on armies. On one hand you've got a great way for regiments to maintain both a teamspeak, and server as well as a community that you know will (or should be able to) maintain their own populations for events, in my opinion the DA, UA etc. are the primary things holding the NaS community together. On the other hand it leads to drama, "monopolies" so to speak on events, and people feel pressured to join in an army or be squashed.
I think they can help, but the community needs to set standards for armies, their events, etc.