Market watchers place a lot of attention on where Warren Buffett parks his money and what stocks he buys.

But it's important to remember Berkshire Hathaway (NYSE:BRK-A)(NYSE:BRK-B), his company, does so much more than buy stocks, as just 22.5% of its $520 billion in assets are parked in equity securities.

So when considering an investment in Berkshire Hathaway itself, its critical to look at all of its businesses, and it turns out one is having a stellar run that we should all take note of.

The big business that could
GEICO is one of Berkshire's most important businesses, and after it was fully acquired in January 1996, Buffett revealed that GEICO was his "first business love."

In last year's letter to Berkshire shareholders Buffett said:

GEICO in 1996 ranked number seven among U.S. auto insurers. Now, GEICO is number two, having recently passed Allstate. The reasons for this amazing growth are simple: low prices and reliable service.

Source: The Motley Fool.

In fact, when GEICO was fully acquired by Berkshire, its market share stood at 2.5% but by the end of 2013, it stood at a staggering 10.2%. And a glance at the most recent earnings data reveals 2014 has been another year where it has only continued to grow.

The strong 2014
Through the first nine months of 2014 the premiums written -- essentially, revenue -- at GEICO have grown by 10%, rising from $13.7 billion last year to $15.2 billion this year. As shown below, this trend is nothing new, as the 2014 levels now stand 45% above the 2010 levels:

Yet it isn't just the revenue which is rising, but also the income, as GEICO's underwriting gain -- the difference between its premiums earned minus the losses related to insurance payouts and underwriting expenses -- has grown from $610 million through the first nine months of 2011 to $1 billion so far in 2014.

In short, GEICO isn't just growing its top line; it is also becoming more and more profitable as well. And what has led to this remarkable success? Buffett added in last year's letter to shareholders:

GEICO's cost advantage is the factor that has enabled the company to gobble up market share year after year. Its low costs create a moat – an enduring one – that competitors are unable to cross. Meanwhile, our little gecko continues to tell Americans how GEICO can save them important money.

The key takeaway
At the end of last year, Berkshire Hathaway had more than 82 businesses it owned outright, and with the various acquisitions throughout 2014 -- Duracell, Berkshire Hathaway Automotive, Charter Brokerage, and others -- that number has only continued to grow.

As a result, it's always critical to monitor the progress of the individual businesses themselves. And clearly the success of GEICO is something that should delight Buffett and all Berkshire Hathaway investors alike.