Yes, my wife and i went a couple times...we did pacific coast stuff actually at the isla de cana which is the closer and much cheaper couzin to coco (jurasic park island).
If you drive down the pacific coast highway south from san jose you will see a few operations on the cost highway. stop early and take the longest boat ride posible to the island (you may see whales).
it is expensive (100 per, plus rentals and park fees) it is super cool though!
I've never boated before, but I have posted a lot on Mountain Buzz!