ProCD, Inc. v. Zeidenberg actually spoke directly to whether a shrink wrap license is enforceable. The Seventh circuit court ruled that it is valid and enforceable, and that clicking "I agree" constitutes consent. I am not saying that is an end all case, but there is legal precedent.
SLAs are a legal contract. Like any contract, certain provisions may be found to be unenforceable based on a variety of factors. Spreading the FUD that EULAs may not be enforceable because they have never been challenged as a whole is not right. It directly contradicts years of legal and commercial precedent.
It also distracts from the real issue of whether or not Apple can limit OS X to Apple hardware as part of its license agreement. As I quoted in an early post, the judge in the Psystar case certainly thinks it's reasonable.