i can say things didn't go well for me. made a backup with itunes 10.4.1 and 4.2.10 just prior to installing iTunes 10.5 beta 9 and ios 5. well, i restored to ios 5 and everything went well until i tried to restore from backup. initially i kept getting a message that said my backup is corrupt or not compatible with the iphone. i then tried restoring from an older iphone backup located from time machine to see if that worked. it didn't. eventually i just brought my backup to my friends computer which had 10.4.1. i put the phone in dfu and restored down to 4.2.10 which worked fine. when i tried restoring from the backup at this point the iphone would just disconnect for no reason in the middle of the upgrade. bummer. thankfully i didn't lose too much because it's all on my computer...i did, however, lose my app organization and settings, text messages etc. i won't be trying to upgrade early in the future, that's for sure. i'm also not sure if i really trust iphone backups anymore. now that i have everything back to normal i've made a fresh backup. let's hope i can rely on it for future updates/restores. edit: aside from the above issues i've been using iOS 5 and it's working great.