The company reported quarterly sales of 15.4 million iPads and 5.2 million Macs, which gave Apple more than 20 million sales of dedicated computing devices. It was reported that HP's sales for the fourth quarter of 2011 were close to 14.7 million, with Lenovo and Dell selling 12.9 million and 11.6 million units, respectively. In addition to that, Apple's figures were twice that of those reported by Microsoft for the same quarter.
Tim Cook, the new CEO of Apple, was asked about the impact of lower-priced tablets in the market, like Amazon's Kindle Fire. Cook replied that he was happy with the iPad's sales and pointed out that sell-through had exceeded sell-in, which left the company with strained inventory levels around the world, contradicting the rumors that the Kindle Fire had dampened potential iPad sales. Cook also stated that Apple sees the iPad as a "huge opportunity for Apple over time" and that "there will come a day when the tablet market in units is larger than the PC market."
Tablets are indeed doing very well with almost every name in the tech world offering their own version of the iPad which pioneered the market. However, I don't think that tablets will ever fully replace computers or laptops. Physical keyboards and mouse controls are too ingrained in people and are also extremely necessary for a lot of computing tasks. Sure you can make keyboard docks and mouse attachments, but what's the point?
Cook also pointed out that the rapid growth of iPad sales was eating up the growth of generic PC sales but not hurting the Apple's own Mac sales. It seems that all of Apple's mobile tech gadgets draw in customers for the company's netbooks and desktop computers. Sales of both have been up, and over 1/5 of all Apple Mac sales were through the company's own retail stores.
Source: Apple Insider - Apple now largest computer maker, sold more iPads alone than HP sold PCs
Slash Gear - Apple sold more iPads than HP sold PCs in Q1 2012