If you grew up in the 1970s and 80s like I did, one of the things you most likely remember about American Express (NYSE:AXP) is the phrase "Don't leave home without it." Delivered from a seemingly endless stream of television commercials and print ads, the clever corporate tag line positively embedded itself in the psyche.

If AmEx's presence in American culture isn't quite what it used to be, it's not because the company isn't still highly successful. It definitely is. And its enough of a good investment that one of the country's most-successful investors is also one of its biggest fans. Thinking about investing in AmEx yourself? Here are seven things you need to know:

1. AmEx is bigger than you think
With almost $157 billion in assets as of March 31, 2013, AmEx is the country's 19th largest bank holding company, putting it ahead of Deutsche Bank AG, the German banking giant's American operation. Size doesn't mean anything in and of itself, but used skillfully, size can help generate revenue and profit far beyond that of a smaller rival.

2. Great share-price performance
Over the past year, AmEx has returned gains of 33.08% to its shareholders: impressive by any normal standard, which these times aren't. For the same period, Bank of America (NYSE:BAC) shares gained 77.96%. Even Citigroup (NYSE:C) is up by 86.97% in the past year. But even given all that, a return of 33.08% is nothing to look down on.

3. Revenue is up
For the first quarter of 2013, total revenue for AmEx was up 4% year over year: this at a time when revenue for some big banks is flat or declining. For the same period, total revenue at JPMorgan Chase and Wells Fargo (NYSE:WFC) was down 3.87% and 1.41%, respectively. Profit is all well and good, but if it isn't born out of ongoing revenue growth, then it's not sustainable.

4. Killer return-on-equity
Return-on-equity, or ROE, is a measure of management effectiveness, and gives you some notion of how much profit a company generates with shareholder money. AmEx's ROE is a staggering 22.99% trailing 12 months. Even the extraordinarily well-run JPMorgan has an ROE of only 11.55%.

5. Amex pays a dividend
Wells Fargo pays a quarterly dividend of 3%, and JPMorgan pays 2.8%. At 1.2%, AmEx's dividend yield isn't much, but it's something -- icing on the cake for what I consider to be more of a great growth stock.

6. Cardmember spending grew
As you might expect, cardmember spending is AmEx's bread and butter, and the good news is that it was up by 6% for the first quarter of 2013. It rose even higher if you take foreign currency translations into account: 7%. 

7. Buffett really likes Amex
Warren Buffett likes his bank-holding companies. Wells Fargo is Berkshire Hathaway's (NYSE:BRK-B) largest holding, and only three spots behind Wells is AmEx. With more than $151 million shares worth more than $11 billion, Buffett's Berkshire holds a 13.8% stake in the charge-card giant.  

Foolish bottom line
You should never invest in a company just because someone else does, even if that someone is Warren Buffett. But when the age's arguably greatest investor makes a company one of his top investments, it's a fact worth serious consideration. Add to that the other six points we've discussed today, and you definitely have an investment worth serious consideration.