After updating to iOS 5 on numerous devices, many people have been reporting that Safari crashes frequently. In fact, many of the default apps including YouTube, Mail, and the Music app are also having frequent crashes. Most of these problems can be solved by restarting your device by holding down the home button and the sleep/wake button simultaneously until the Apple logo appears. However, for Mobile Safari specifically, here are some tips that might stop Safari from crashing on iOS 5.
Step 1) iCloud bookmark syncing initially uses a lot of resources when trying to accomplish the first sync. To fix this issue, simply go to Settings > iCloud and toggling Bookmarks from "On" to "Off." After a few minutes, go back in Settings and switch the toggle back to "On." Your bookmarks should still be synced and Safari should stop crashing as frequently.
Step 2) Sometimes the app needs to be completely terminated, you can accomplish this by closing Safari, double tapping the home button and tapping and holding on Safari. Click the icon in the top left corner to officially terminate Safari and all of its active processes.
Step 3) For a few users, upgrading to the newest iOS version can also solve your problem. Go to Settings > General > Software Update to initiate the upgrade.
Step 4) Turn off all iCloud syncing by going to Settings > iCloud and tapping "Delete Account" at the bottom of the screen. If this fixes your problem, feel free to try and re-add your iCloud account, however, your mileage may vary.
Step 5) If none of these solutions work, you will have to restore your device following this guide here. It is a good idea to set up your iDevice as new in order to avoid the crashing problem from reappearing.