During the week, our Motley Fool Twitter feed (@themotleyfool) shares lots of articles. In case you missed it, here are the top five most popular articles that were tweeted this week.

5. @themotleyfool: It didn't need a bailout. Its cars get great reviews. So why are Ford's (NYSE: F) sales eating GM (NYSE: GM)and Chrysler's dust? mot.ly/o1vfD7 

Ford, General Motors, and Chrysler all posted solid sales gains in September. However, with General Motors selling trucks like hotcakes, Ford's sales numbers simply weren't as impressive. What's behind the slower sales at Ford?

Read the article to find out why Ford might be lagging behind other American automakers.

4. @themotleyfool: Why the future of music might not sound quite so harmonious to Apple's (Nasdaq: AAPL)$AAPL iTunes: mot.ly/oRDatD 

A new service may be here to disrupt the music industry. Spotify -- a cloud-based music service -- recently launched in the U.S. and has attracted 2 million paying subscribers with its freemium model. Other music companies, such as Sirius XM Radio (Nasdaq: SIRI) and Pandora Media (NYSE: P), might need to come up with a response, since Spotify is gaining traction domestically and already has a large base in Europe.

Read the article to see what’s behind Spotify's growth.

3. @themotleyfool: What's the worst that could happen if Greece goes belly-up? (More than it already has, we mean.) Plenty:  mot.ly/oG5bcs  

The debt crisis in Greece continues to dominate the headlines. If we face the fact that Greece will probably default, what is the true cost of that default? Fool Sean Williams takes a look at Greek debt exposure at various European banks. And his conclusion might surprise you.

Read the article to see whether a Greek default will affect the world economy.

2. @themotleyfool: Got questions about that $AAPL iPhone event? Talk it out in our (now actually functioning) live chat:  mot.ly/nTgnil (560)

On Tuesday, we covered Apple's iPhone event. Everyone expected the announcement of the iPhone 5, but instead we were treated to the iPhone 4S. Apple also unveiled several new features and apps, including the much-discussed Siri.

Read the article to see the transcript of our live coverage and our take on Apple's announcement. (We also have a tribute to Steve Jobs, who passed away a day after Apple's iPhone event.)

1. @themotleyfool: Though he announced it publicly, many people missed this stock tip from Warren Buffett.  @The_Bull_N_Bear  didn't:  mot.ly/oYQPMe

Recently, Berkshire Hathaway (NYSE: BRK-A)(NYSE: BRK-B) announced that the company will repurchase shares, indicating that Berkshire stock was undervalued. Yet investors seem to be ignoring this opportunity that Buffett has presented. Fool Alex Dumortier thinks that's a big mistake.

Read his argument about why Berkshire Hathaway shares are undervalued, according to Buffett himself.

Be sure to follow @themotleyfool on Twitter for your daily dose of Foolish investing news.

The Motley Fool owns shares of Apple, Berkshire Hathaway, and Ford. Motley Fool newsletter services have recommended buying shares of General Motors, Berkshire Hathaway, Ford, and Apple, as well as creating a bull call spread position in Apple. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.