A recent report found that for smartphone users apps are 6 times more popular than web browsers; for tablet (such as the iPad) the difference is less extreme - only a 60/40 split - but still prevalent:

The study, conducted in April 2011, found that on smartphones, apps were used 85% of the time, but the Web browser was used just 15% of the time. On tablets, apps were still popular, but were used just 61% of the time as compared with Web browsing, which was used 39% of the time.

There are two key takeaways on this:

There is a difference in the way smartphones and tablets are used. Not a surprising conclusion, but an important one to bear in mind when developing your mobile strategy.
People prefer dedicated apps for specific, common tasks. Many of the apps that are "more popular" than web surfing and email are, essentially, just narrowly-focused versions of web surfing and email. For example, people prefer using the LinkedIn app to accessing LinkedIn via the web browser, even though both offer ostensibly the same capabilities.

I can verify the second point through my own experiences. There are several online resources I use very frequently, that currently do not have an app. Accessing them via browser is becoming problematic because it interferes with other, non-reoccurring web use; it is hard to save my in-progress work, for example, because every time I open a new link I loose my place.

This is important to bear in mind when deciding whether to create an app or a mobile website. If you expect customers to use your tools on a regular basis it may be worth creating a dedicated app, even if it is just a specialized web browser.