I just got back from a trip to London. I was only there for a few days, but in that time I spent more than I have spent in any two equal length business trips within the US. My fairly ordinary hotel room cost nearly $350 per night. At that price do you think they would throw in Internet access? Not a chance. Add another $30. Coffee at Starbucks, $6. Nothing special, just a venti coffee.

That's what a weak dollar does for (to) you in the global economy.

When a currency is weaker, it means that it will buy less of what it could previously buy. Another way of saying this is it takes more (dollars, in this case) to buy the same things it could before, whether it be hotel rooms or coffee at Starbucks.

My trip to London was made worse by the fact the British Pound is trading strong in world markets. It takes fewer Pounds to buy a Dollar today than it did a couple of months ago. Unfortunately the strong Pound doesn't necessarily translate into cheaper British goods. Not for travelers at least. London is notoriously expensive to begin with; but now that they're ramping up for the Olympics in 5 years' time, an already tight real estate market is pushing prices even higher.

But why should you care, especially if you're not going to London?

For one thing, just as a weaker dollar cannot buy as much hotel room in London, it cannot buy as much of things produced in foreign countries and brought here for sale. Dollar prices on foreign goods tend higher when the Dollar is weak.

But the news isn't all bad. Another reason to care about the weak Dollar is that US companies doing business overseas bring more Dollars home. If my London hotel happened to be a Marriott, the huge sum of money I spent there, net of operating costs, looks every bit the equivalent of dropping $350 a night at a Fairfield Inn near the Des Moines airport. The weak Dollar tends to boost earnings at US companies doing business overseas.

As an investor, you probably haven't missed the news we're in another round of earnings announcements. The news could be better than expected this season because of the weak Dollar. And that, my friend, is why you should care about the weak Dollar.