I just finished leafing through the latest Current Index of Legal Periodicals (CILP) which I receive electronically once or twice a week. It reports all new articles published in law reviews and journals, broken down by subject matter. Personally, I've always skipped the subject-matter headings and gone straight to the full listings of tables of contents at the end of each CILP.
Over time, I have noticed that the CILP has become mostly irrelevant to me, as I decreasingly find new articles worth scanning, let alone printing for a full read. This is not to suggest a decline in the quality of new law review articles. Rather, I find almost everything I need or want to read on the Social Science Research Network (SSRN) months (at least) before those papers are published in law journals. The only significance for me of final publication is the correct citation for the article, and even that is not strictly necessary because citations to SSRN working papers seem perfectly acceptable to most publishers.
What, then, is the value-added of final publication in law journals? For one, there is always the risk that a paper will change substantially between its initial publication on SSRN and its final publication in some law journal. Many authors will solicit or simply receive comments on the working papers they post on SSRN, and amend their papers accordingly. However, that risk is mitigated to some extent by the possibility of uploading updated versions of papers to SSRN, which is something I have done regularly.
Another consideration is the very substantial editing process that articles go through once they are accepted for publication in law journals. I'm inclined to discount the importance of that editing process because, in my experience, for any given paper there is at best a 50-50 chance that law-student editing actually improves it.
Far more importantly, final publication in a law journal is vital to junior faculty members in the promotion and tenure (P&T) process because self-publication on SSRN does not count as publication for P&T purposes. Apparently, acceptance of a paper by a group of second-year student law review editors provides a crucial proxy for law faculties, which will not as a rule accept an SSRN publication, even if accompanied by gushing letters of praise from a gaggle of Nobel laureates.
Along the same lines, final publication in a law journal provides a market signal to the legal academy of the quality of the article, based simply on where it is published. An article published in the Harvard Law Review is almost irrebutably presumed to be "better" than one published in some "lesser" journal. In reality, this is nonsense. I say that, of course, as someone who has never published in the Harvard Law Review.
None of the reasons presented above for final publication of articles in law journals is particularly important to me or my own work, and should not be relevant for most experienced researchers. When conducting research, I'm happy to rely for the most part on my own sense of the quality (or lack thereof) of papers I read on SSRN. When reviewing papers outside my own limited areas of expertise, I usually will ask others whom I trust for their opinions. For me, those trusted friends and colleagues are far more valuable and trustworthy proxies than all student law review editors combined.
I don't suppose we'll ever do away with law journals or other forms of final publication mainly because of the practical purposes they serve in the P&T process. For many researchers like me, however, final law review publication remains important only as a source of page cites.