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Most startups start small, thinking to expand after learning some valuable lessons, including making sure they're not releasing bad products that could sink the company or making bad decisions that could do the same. Toward that aim, most startups focus on building one product at a time, which may be their only product for the first several years of the business.

But there are pros and cons to selling only one product. For some startups, it may make sense to stay focused on one product, where others would be happier and more successful if they sold multiple products.

When Apple's new desktop-focused Mac App Store launched, it was expected to be a hit. One day later, Apple confirmed that the store was taking off, with over 1 million downloads on its first day. But how many of those were free apps? How many were copies of Twitter for Mac or Angry Birds? What about individual developers' results?

As it turns out, many Mac App Store developers are sharing details about their Mac App Store sales figures, both on their own websites and in traditional forums. Below is a selection of those results. Spoiler alert: the news is good.

Microsoft has finally released sales data on its newly launched mobile operating system Windows Phone 7...well, sort of. Instead of revealing actual numbers regarding phone sales to consumers, it has announced that its partner handset manufacturers have sold over 1.5 million devices to carriers and retailers in the first 6 weeks the phones have been on the market.

That helps Windows Phone 7 "build customer momentum and retail presence," says Achim Berg, Microsoft's VP of business and marketing for Windows Phones.

Great, so what does that really mean in terms of platform success?

Don't worry - Apple isn't trying to launch the next Foursquare - but the company has developed its own check-in service that integrates with Apple's in-house applications. The new service went live this week.

The lineup of Apple-owned applications that make up the service includes "Concierge," a push-enabled app used by employees to receive notifications of customers with appointments entering the store and an app called "Scout" used by managers to establish precise physical locations within the store as part of the setup process.

Given the brisk sales of Kindles, Nooks and iPads over the last few months, it doesn't come as a surprise that the sales of e-books are also flourishing. According to the Association of American Publishers (AAP), e-book sales for January to August are up from $89.8 million for 2009 to $263 million in 2010. This 193% increase in sales means that electronic books now account for almost 10% of consumer book sales in the U.S., up from just 3.31% in 2009. All of these numbers exclude textbooks and other academic texts, so the actual numbers are likely even higher.

Consumers will have downloaded 25 billion mobile applications to their smartphones by the year 2015, claims market research firm Juniper Research in a report released today. That's an increase from less than 2.6 billion applications in 2009.

Part of this projected increase is due to the launch of additional "app stores" worldwide, including those in large markets like China and India. However, cautions the report, just mimicking Apple's model alone may not be enough. "Customers are buying the iPhone for the apps," says report author Dr. Windsor Holden. "That's not been the case with other handsets."

Apple announced this morning that it has sold over 1.7 million units of the new iPhone 4 smartphone through Saturday, only three days after its launch on June 24. These numbers, touts the Cupertino-based company, make the iPhone 4 launch the "most successful in Apple's history."

Oddly enough, it's also the launch that seems to have had the most technical issues as well, like, for instance, the antenna reception problems Apple confirmed both officially and unofficially last week. Holding the phone in a particular way leads to a weakened signal and sometimes even dropped calls, according to numerous reports from new users, testers, gadget blogs and mainstream media news outlets.

Sprint made a big miscalculation when it initially released the first-day sales numbers for the new HTC EVO 4G smartphone, the highly anticipated Android device that has been positioned by many as the first real competitor to Apple's iPhone. Originally, Sprint announced that the total number of devices sold on launch day was three times the number of Samsung Instinct and Palm Pre devices sold over their first three days on the market combined.

Today, however, Sprint is saying its original report was in error. Sales numbers were actually in line with the number of Instinct and Pre devices sold over the first three days on the market combined, not greater.

An interesting chart released from Morgan Stanley Research this morning shows that during the month of April - the month the iPad launched - netbook sales stalled. Did the iPad really have that much impact on an industry that was once the fastest-growing segment of the PC market? Or was the netbook's fall from grace bound to happen at some point, with or without the Apple tablet's help, as consumers discovered how hard it is to type on those tiny keyboards?

Buyers outside the United States who planned on buying iPads are going to have to grit their teeth a while longer yet, as the release date has changed.

Based on the strong U.S. demand for Apple's new iPads, the company has decided it would delay the product's international release for a month.