How safe/secure is the data saved in html5's localStorage?
I understand that its acceptable to store & retrieve "non-secure" data such as language or font-size preferences and that information is freely available to anyone with access to that browser, but how about more sensitive/private data such as names, addresses and phone numbers?
For instance, would storing a user's phone number to later auto-populate various forms on a website constitute any breach of privacy/security? Also, are there any further implications/issues with this sort of data storage?
I personally wouldn't store anything personal like that for auto-population [or anything else]. Modern browsers will auto-populate if they're set to, but some of us [I for one] don't like auto-population and if you stored and populated the info for me when I have my browsers all set to not do it I would probably be turned off by your site.
Also, if you're not using an https connection 100% of the time the information will be sent from the users computer to your site automatically "in the clear", which means if they're somewhere public with an open wi-fi their information could be compromised without them knowing or even having the option to stop it from happening.
For those and some other reasons, I'd give auto storing/sending anything personal that way the thumbs-down.