Terms of Service, Enforceable or Not?

What's the difference between clickwrap and browsewrap?

• ABrowsewrap is encrypted; clickwrap is not
• BClickwrap requires explicit agreement (checking 'I agree'); browsewrap claims agreement merely from using the site, courts consistently uphold clickwrap, but are much more skeptical of browsewrap
• CClickwrap is older
• DThey're identical