Analysts are predicting that by 2015 there will be more tablets than PCs in use in the US, and Apple is already so far ahead of the crowd that the other tablet makers will struggle to catch up.

Yankee Group predicts that tablets, including the iPad, will climb from 25 million in 2011 to 134 million by 2015.

The iPad already holds 51% of the tablet market in the US, so Yankee Group claims that the other tablet makers are battling for less than half the overall market.

Yankee Group research VP and head of the devices practice Carl Howe said: "For the second quarter in a row, Apple's iPad is leading the tablet market, forcing all other competitors to battle for the remaining 49 percent share.”

However, almost 25% of respondents in Yankee Groups research who intend to buy a tablet in the next six months said they don't know what brand they will purchase, so there is a “huge opportunity for manufacturers looking to grow their base”, according to the research firm.

"It's too late to change current ownership, but tablet makers looking to gain on Apple need to start improving their brand visibility and targeting people who don't already have their minds set on an iPad," said Howe.

Read Andy Ihnatko's thoughts about Apple's post-PC world