According to T-Mobile USA, G1 Android users downloaded an average of at least 40 applications for their phones while iPhone users averaged about 37 apps. There is no data as to retention of apps - G1 users may have downloaded their 40 apps, only to keep half that number, while iPhone users may retain more on their device, and vice versa.
What we DO know, however, is that the Android Market is alive and well with G1 users digging into plenty of the apps offered there. Further data suggests that 80% of G1 owners download an Android application at least once per week.
Whether it's Google's Android Market or Apple's iTunes App Store, the model for offering apps from third-party developers in one convenient, easy-to-use location seems to be successful. What has your experience been like using the Android Market?