They're an interesting villain from a sci-fi standpoint but I don't think they fundamentally represent anything, besides the classic concept of an emotionless enemy who can't be bargained or reasoned with and doesn't feel pity or remorse or fear.
They went through some revision during production - they were originally envisioned as a hive-minded insectoid race, but the budget wouldn't allow it. That's interesting, because a hive-minded race is simply existing in its natural state, whereas the Borg allow for the possibility that they began like any other species and had collective consciousness imposed upon them.
I think the threat represented by the Borg is ubiquitous enough that any viewer can impose their own political interpretation upon them.