The San Francisco Chronicle is citing the "ChoicePoint Effect", which means that more companies are willing to fess up when something goes awry with personal information. The article suggests that we aren't more data incidents, we're just hearing about them more often.
I'm not entirely sure this is the case. I have a feeling that the number of incidents has increased and we are hearing about it more often. ID theft is being perpetrated more and more often in recent years and I think that more criminals are seeking out personal information than they did before. A mugger would take your wallet and use your cards until you reported them stolen. Now, using the same stuff that's in your wallet, they're opening accounts in your name and committing a different species of crime. When personal information can be acquired in bulk, whether from dumpster diving or impersonating legitimate businesses, the sheer number of threats faced has to have increased and the number of incidents along with it.
The Chronicle article is here: Security breaches not on rise / Privacy watchdogs say incidents are being disclosed more often.