Last time this already helped me out, so probably will help you out as well. Try to reinstall iTunes and the MobileDeviceDrivers with this description: http://support.apple.com/kb/HT1747
All iTunes content - of course - will not be harmed.
I could repeat the problem by doing the following steps:
1. Open a GoogleApps Maillogin-Page (e.g. m.42.gd) and notice already that any entered character disappear in the textfields. The checkbox acting weird.
2. Open any other page (e.g. amazon), let it load.
3. See no change in the page content. If you close Safari and open it again the page appears. Now you see even Javascript did not run properly on the page as there are loading spins…