There is an important recent decision upholding web-wrap agreements. Register.com v. Verio http://www.icann.org/registrars/register.com-verio/decision-23jan04.pdf.
In that case, one of the three appeal judges died while writing the decision. (He was dissenting). This case has special circumstances -- repeated use of website and bad conduct -- so even though it is from an important court, I am not sure if it will be followed in all circumstances.