There are at last two good reasons to "leave well enough alone":

1. The more obvious one: although (most) apps on Ovi are safe in this regard, there are a few relatively well-known apps that will lead you straight into reboot loop Tartarus. This becomes exponentially more likely, the father you deviate from the beaten Ovi path.

2. The second reason is ostensibly more subtle, but can cause much greater frustration over time.. Unfortunately it can be caused by many more apps, including ones on Ovi (and elsewhere) that may even be quite popular. Those are apps that may be resource hungry in general our frequently use power-expensive services (GPS, network, etc) that willsignificantly reduce your phone's uptime on one charge. worse yet, they may install services that are tough to find but also frequently use said services. After a number of apps has been installed, you suddenly notice idle mode using upwards of 150 mAh, where previously it was maybe 20-30. Your phone goes from full charge to low battery mode within a few hours.

The n9's battery appears anemic given its low total output rating; but the N9 makes up by remaining very power efficient for the most part and still manages to deliver some respectable talk/standby/uptimes. This fragile balance is easily undermined by said apps.