i've just finished episode 11 of season 1 of battlestar galactica and here is my theory on the cylon's plan:
they're helping the peeps get to kobol so they can show the cylons (unintentionally) how to get to earth so the can take over earth too. cylon boomer and helo (RAWR!!) on caprica are meant to propagate a species of human/cylon while the cylons deplete earth so they'll have somewhere to go back to. and they just bounce back and forth between the two whenever one is depleted.
can cylons even have babies? i don't know yet.
ok. geek talk done.