I think Carnival's tipping policy is a good and fair one. $10 per person per day is fair and reasonable. And yes, it goes directly to the staff involved, not the cruiseline. Lizard has provided the correct breakdown.
PREPAID TIPS - This amount can be paid when paying for your cruise. As Serene pointed out, It cannot be adjusted up or down or removed once on board.
AUTOMATIC TIPPING - This is the first entry on your Sail & Sign account. It can be adjusted up or down or removed. (Hopefully, nobody actually does that.) It's certainly a fair amount when you consider all these folks do to make our cruises pleasant.
ADDITIONAL TIPPING - Some like to leave their automatic tips in place, and tip a little extra to their cabin steward and/or waitstaff in the dining room. Not necessary, but appreciated. The room service delivery person should be tipped a small amount ($1-2) each time you use their services.
BEVERAGE TIPPING - Whenever you order a drink, it will be charged to your S&S card, and a 15% tip will be automatically added. So - unless you just want to, you don't need to tip the bartender extra.
Personally, I think the tipping is just about right. I leave my automatic tips in place, and tip a little extra here and there, or on the last evening. I think the cabin steward, in particular, earns and deserves his tips. He's in the cabin at least twice a day, cleaning, making beds, providing new towels, filling ice buckets, leaving mints, Capers, and other info in the cabins, and making those adorable little towel animals. Plus, he's on call most of the day, with a mere press of a button. Love those guys!