Sorry, I meant to say the PiiBot can randomly repin/like/comment, it doesn't auto follow at the moment (I will update PiiBot to do that in a couple of days).
But in regards to the limit they have started imposing (they have started limiting comments too) there is nothing stopping some one from having multiple accounts promoting the same links or targeting the same keywords and slowing the pining/following/liking/commenting down on each account so it doesn't hit the limit.
Although they still haven't imposed a limit on the number of Pins that can be made, one test I ran pined over 2000 pins in an hour to a single account.
The only problem in pining that quickly is that any one who follows the account will quickly unfollow it since the amount of pins being made will flood their "Recent Activity".