Ian Ramsay has self-archived "SSRN and Law Journals—Rivals or Allies?" in SSRN.
Here's an excerpt:
The author identifies and evaluates the respective merits of publication in law journals and publication on the Social Science Research Network (SSRN)—the largest open access repository for legal scholarship. This evaluation leads to the conclusion that at this stage of the evolution of law journals and SSRN, there are advantages in authors publishing both in journals and on SSRN. However, publication on SSRN can have particular advantages for authors in smaller countries.