There is a small feature in iOS 5 that can get simply annoying, inconvenient and can get your iPhone to run out of space. In fact, the first time you notice you could think that somebody has been downloading apps without your permission. But how did this happen?
Since version 4.3.3, the standard behaviour is that every time you download an app from iTunes on your Mac or PC, this purchase will be synchronised directly on the iDevice using that iTunes account. For families sharing iPads or iPod Touches, it means that when daddy buys a Poker game, it will automatically be downloaded to his iPhone but also to his five-year-old son.
There is an easy solution for every user without needing to tinker too much with the device, but I recommend you check the settings on both your desktop and mobile devices. I also suspect that when iTunes asks you to verify your identity asking for your iTunes ID password for no reason, it's getting ready to sync. On your Mac, you only need to go the preferences window on iTunes and right under the Store tab - with that green shopping bag - you can select which type of purchases to download automatically. Just make sure automatic downloads are unchecked for apps.
On your iPhone, iPad or iPod Touch, disabling automatic downloads is also easy. In my case I've chosen to allow my laptop to sync and I simply switch it off on my iPhone. This can be useful if you want your iPad to get the latest games, but not your iPhone when you're out and about. Simply tap the Settings icon, scroll down to Store and chose the type of content you want to have downloaded automatically: music, apps or ebooks.
It's also worth noticing that app downloads are limited to 20MB, just like when you buy them directly from your device and you are connected to a 3G network. Obviously, Wi-Fi will take care of those waiting to be downloaded as soon as a strong network is available.