In connection with Brower v. Gateway 2000, Inc., it's worth noting what courts have done and why in the past few months in other states with similar issues. Those decisions are the topics of three blog posts here, here, and here. My students might recognize the author.
And, to confuse matters even further, there's this and this.
My students desperately want an answer -- is an online mandatory arbitration agreement enforceable? And all I can tell them is: it depends. It depends in part on which state you're in. It depends in part on the method that is used to show the buyer's agreement. It depends in part on whether class arbitration is available. It depends in part on how bad the alleged wrong is and how much merit the plaintiff's claim appears to have. What I can teach my students is the arguments on either side and the ways they are strengthened and weakened under different facts. But if they're looking for black and white answers applicable in all situations in all states . . . well, being a lawyer isn't for them.