According to Gartner, Apple's nearly 20% rate of unit sales growth rate over the year-ago-quarter helped to push Apple into the top 5 vendors (by unit volume) in Europe. Apple now stands at #5 in unit sales. Over the same period, three of the top five vendors (HP -7.5% to 21.8%, Acer -45.1% to 24.5%, Dell -10.0% to 9.6%) experienced an absolute decline in unit sales. Only Apple (having sold 5.7% share of units sold in Western Europe) and ASUS (at 7.8% unit share) enjoyed gains, each about 20% over the period.
In the UK, Apple is a top-5 vendor (ranking #4, at 7.8% of unit share) by volume; in Germany and France, Apple is not ranked. Western Europe bought about 14.8 million PCs in 3Q2011, and there's quite a bit of that market Apple hasn't snagged.
This market doesn't include the tablet market in which Apple's iPad competes.
Of course, unit share isn't profit share. Apple doesn't sell an undifferentiated commodity box; it competes in a high-margin segment of the PC market. Apple's gains in PC share represent even greater gains in the share of the profit to be had in the PC business in a given market. And as the Western Europe numbers demonstrate, Apple has opportunities for future growth in the PC business.