Be careful when some tech companies brag about their 'mobile' business.

Even as Facebook was struggling to make money on mobile, a challenge that its third-quarter results may help put to rest, there was never any doubt that the social network was among the mostly widely used applications on smartphones and tablets.

Compare that to the experience of tech giants such as eBay, Intel and Dell. Each suggests it has a mobile business, but it isn't so clear-cut. The rush to drape businesses in a 'mobile' cloak is reminiscent of the dot-com era when everyone seemed to be talking about their 'Internet' strategy.

Ebay, for example, expects its PayPal unit to do over $10 billion of 'mobile payment volume' this year. That excites many investors, who think it shows that PayPal can expand its business from online payments to the much larger market for in-store payments.

But what eBay refers to as 'mobile payments' are mostly just standard e-commerce transactions happening on tablets or smartphones instead of on a desktop PC. It is hard to get excited about PayPal's traditional e-commerce business mostly following consumers' changing Web habits.

Ebay is experimenting with products more closely aligned with what most think of as mobile payments. For instance, it is allowing small merchants to accept credit cards on smartphones and enabling consumers to pay without physically swiping a credit card.

But Square is ahead of PayPal in working with small merchants to process cards. And while more retailers now accept PayPal, consumers need to enter a phone number and PIN, more cumbersome than simply swiping a card. So the impact of these initiatives is likely limited so far.

Dell splits its computer business into 'Desktop PCs' and 'Mobility.' But it doesn't sell smartphones and its tablets have failed to capture meaningful market share. So what is in the 'mobility' bucket? Mostly laptops, which buyers are increasingly shunning in favor of Apple's iPad.

Dell hopes to grab tablet share with devices running Microsoft's new operating system that works with touch-screens. But its new tablets will go against similar ones from, among others, Hewlett-Packard, Lenovo and even Microsoft, which is releasing its Surface tablet this week.

Then there is Intel, which in 2011 began describing its business selling servers with a new adjective: 'mobile.' The justification is that as mobile devices multiply, data centers need to be outfitted with more servers to handle increased Internet traffic.

That trend has helped Intel boost its data-center segment faster than its PC segment. Yet that is little consolation for investors, considering that nearly two-thirds of Intel sales still come from PC chips. Demand for these is sagging as market share goes to tablets and even smartphones. Intel may dominate in PC chips, but when it comes to mobile circuitry, its share is negligible.

Mobile is today's digital tsunami. Some companies are ready to ride the waves, others may see parts of their business washed away.