Are ToS considered contracts in and of themselves, enforceable under contract/civil law?
Generally I'm talking about the Common Law systems in the major regions (UK, North America and Oceania). Anything that applies to (majority of) Europe would be fine too.
Providing they meet the basic requirements (see What is a contract and what is required for them to be valid?) then they are binding contracts.
Consideration is not an issue: the site provides the content, the user provides eyeballs on it.
Consent is the major stumbling block.
Online Terms of Service are either presented as browsewrap or clickwrap or sign-up wrap. A browsewrap provides notice of the terms of service but there is no specific user assent to them. A clickwrap requires the user to check a box specifically about agreeing to the terms (with or without user registration). A sign-up wrap presents user registration with a "Sign up" and provides notice to the terms at the point of service but doesn't have a check button specifically for the terms.
As an example, Stack Exchange provides two types of wrap. For the casual user, there is a Legal link at the bottom of the page - a browsewrap. If you sign-up, you go to a page that says "By clicking "Sign up", you agree to our terms of service, ..." - a sign-up wrap.
Whether a Terms of Service is an enforcable contract depends on whether the user provided notice, whether the user gave consent and whether enforcing the agreement is conscionable. Clickwraps and sign-up wraps have the advantage over browsewraps in the first two of these.
Assuming that the contract terms are unremarkable (i.e. they are within the range of "normal" for that type of contract) a clickwrap will normally create an enforcable contract - Forrest v Verizon and Motise v America Online being the relevant case law. Browsewraps are more problematic: Specht v Netscape said no contract but where the browsewrap is shown prominently and repeatedly they can form an enforceable contract - Hubbert v Dell and Cairo v CrossMedia Services. Zaltz v Jdate was a sign-up wrap and did create an enforceable contract.
All of these turn on the facts of how the information was was presented to the user. For example, in Meyer v Kalanick the Second Circuit said:
Where there is no evidence that the offeree had actual notice of the terms of the agreement, the offeree will still be bound by the agreement if a reasonably prudent user would be on inquiry notice of the terms.[sic]
So, in general, Terms of Service are enforcable as a contract if a reasonably prudent user could, on inquiry (e.g. by clicking a link), make themselves aware of the terms. This also explains why skrinkwraps (when software came on actual physical media in a shrink-wrapped box with the terms inside) were not enforcable - a reasonably prudent user could not inform themselves of the terms without unwrapping a product they didn't yet own.
Yes, terms of service (TOS) are considered contracts. The website or other entity has offered you use of their service in exchange for your adherence to their terms of service. You signify acceptance of the contract by use of the service. Normal contract interpretation, termination, etc will all apply, per the jurisdiction that applies (look for a choice of laws section in the terms of service, then look in your local jurisdiction's laws to see if the choice of laws clause is valid).
There are many exceptions depending on the jurisdiction, for instance if you don't have a French translation, your Candadian TOS may not be valid in Canada, but on the whole, TOS's are considered contracts and probably enforceable.
