Here are some assumptions on my part:
1. It used to matter, especially pre-tenure, where one published one's work, because electronic databases like Westlaw and Lexis were expensive, and so one's work would receive more attention if it had been published in law reviews to which key players (judges, other academics, and attorneys) were likely to subscribe.
2. SSRN, Bepress, and websites generally now make it easier for researchers to find articles without having to pay for Westlaw and Lexis searches or having to maintain a lot of subscriptions for major law reviews.
3. Certain specialty law reviews get more attention from key players than do certain general law reviews. For example, I'm more likely to read something published in the Georgetown Journal of Legal Ethics than in [insert name of general law review here].
4. Law review publishing takes time. Lots of time. Articles come out long after they're written, and some articles lose traction because of the delay. Blogs, on the other hand, provide immediate gratification due to immediate (or near-immediate) publication.
5. Blogging as scholarship is still new. Some folks believe that the major players aren't, well, playing yet:
The other main limitation of blogs as forums for serious scholarly
debate--tactfully not noted by Kate [Litvak]--is that only a miniscule number of
first-rate legal scholars in any field actually blog on scholarly topics;
indeed, if you subtract the Chicago faculty blog and Balkinization, "miniscule"
may overstate the number of leading lights in their fields who blog in their
areas of scholarly expertise (you can probably count the remainder on one
hand). I find it hard to see how blogs can have much significant scholarly
impact when the most significant scholars rarely participate in the forum, or,
at least, rarely participate for scholarly purposes.
Brian Leiter, "Blogs as Scholarship" Conference at Harvard. My guess is that we'll need some more empirical work to figure out if more and more big names are blogging--and whether blogging is actually a great way to turn some great people into bigger names than they'd be w/o blogging. (Am I the only one who remembers that, for almost all law reviews, third-year law students select which articles get published and that, for many of them--and formerly many of us--their decisions may stem as much from personal preference, of the "I hate Subject X" variety, and from eyeballing the ease of editing and cite-checking as they do from an understanding of what makes an article important?)
Here's my rather long-winded point: the discussion of how best to develop and disseminate scholarship that counts (i.e., gets used) is important, but as we start shifting the paradigm away from traditional top-50 law reviews (and why that cutoff number?), we run the risk of moving to downloads as yet another number to feed into the USNWR rankings. (See Jeff Harrison's Which Tail Wags? post.) Once we use downloads--or even "top 50 reviews"--as a shadow variable for the real issue, we're in real "angels dancing on the heads of pins" territory.
The real issue: is our scholarship of use to some community, whether that community be other academics, judges, legislators, attorneys, or students? If it's not, why not?