Second up tonight at our Publishing Apps event in London was Simon Podd from mobile analytics firm Flurry, which has a central vantage point in how apps are being downloaded and used on smartphones and tablets.

Currently, one in three new apps are using Flurry’s SDK, so it’s tracking a lot of data – 36bn app sessions a month. On with the stat-bombs…

Flurry tracks 529m active smart devices – smartphones and tablets – up from 71m in July 2010, and 319m in July 2011. Podd suggested this is still early days. “There’s another potential 1.5bn smart devices to be sold out there…” Podd added that around 20% of these smart devices are tablets.

Flurry estimates that in April 2012 more than 1m apps were available across Android’s Google Play store and Apple’s App Store – 600m on iOS and 460m on Android. But he warned that Android is monetising less well than iOS: “For the same number of users per platform, for every dollar generated from the Apple App Store, you would only see 24 cents from Google Play.”

Flurry’s stats indicate that 49% of time spent with apps is spent using games, plus 30% in social networking. Entertainment apps account for 7% of time spent, News 6%, and other categories 8%.

Where are app users based? The biggest market is the US, where 109m iOS and Android users are running apps, but Flurry says China is now the growing market – app sessions up 870% between January and October 2011.

When are people using apps? “Peak time is any time,” said Podd, noting that there isn’t the same obvious spike in the evenings as for TV. However, Flurry’s stats indicate that app retention is touch. After one month, only 38% of people who’ve downloaded an app are still using it. After six months, it’s 14%, and after 12 months, it’s 4%.

Books specifically. There are 25,000 apps in the iOS App Store’s Books category – under 5% of its total. But Podd noted that the Books category has grown by 255% for sessions and 163% for active users between May 2011 and May 2012 – more than Entertainment, Games, News and Social.

Flurry has split the category up into audio books, comics, stores/libraries and traditional books. For paid apps, 64% are traditional. “Clearly people are more than happy to continue to pay for great content,” he said. “When you look at free apps, there are less traditional content apps being provided: there’s much more focus on the discovery apps, on the stores, on the libraries.”