Modern day pirates are not a joke, but pirates seem more reluctant to try to take on a cruise ship due to its size and the shape of it. The ships do go into a heightened security state while passing through areas known to harbor pirates. Places such as the Gulf of Aden In the area where these pirates work hundreds of ships pass through each day and really less than 1% have been attacked. So really the threat is less than you might think.

With the high straight sides of the cruise ships they are almost impossible to climb and that is how a pirate would access one of these large ships. Ships have taken to closing off the decks while passing through the gulf area so that there is no way to reach the passengers. the Somali pirates use automatic rifles to hijack the ships and keeping passengers below and in the interior of the ship will keep them safe.
So it looks like they are protecting the passengers and keeping them out of harms way.

As most people know, the media hypes bad news and pirate attacks are no different than if a baby dies. Most cruise ships stick to protected waters and usually don't stray off course. These waters are protected by the government and pirates unless suicidal won't go there. The thing to worry about is if your cruise ship goes into international waters, where no one country has the rights to protect it.

And to answer if I would feel safe on a cruise ship, I would almost definitely, aside from the scare of sickness and claustrophobic-ness. These attacks aren't to worried about and just for some added knowledge, cruise ships that travel in international waters have guns and people trained to use them.

I hope this helps, but on a personal note: cruise-ships are bad vacations.