So what's the problem? A systemic lack of safeguards against fraud. In other words, you have basically zero recourse if an 11-year-old in Turkmenistan decides to hack you and caper off with all of your bitcoins. Anecdotally, users have been hoodwinked out of millions upon millions of dollars' worth of bitcoins, and one news anchor even got ripped off when he accidentally flashed his info on live TV.
"Up next: weather, our Social Security Numbers, and the cameraman's wife's bra size. Stay tuned!"
Sure, you can store your bitcoins offline, but that presents its own set of challenges. Just ask this poor bastard in Wales, who procured 7,500 then-worthless bitcoins in 2009, stored his account information on an old hard drive, forgot about it, and accidentally threw it out this past summer, leaving a few million dollars stuck under a landfill.