NZ PC World: Google Submission Hammers Section 92A [proposed NZ DMCA type regulation]:

Google has made a detailed submission to the Telecommunications Carriers Forum that heavily criticises the draft code of practice for ISPs in relation to section 92A of the Copyright Act.
In its submission, Google notes that more than half (57%) of the takedown notices it has received under the US Digital Millennium Copyright Act 1998, were sent by business targeting competitors and over one third (37%) of notices were not valid copyright claims.

With regard to businesses targeting DMCAs agaisnt competitors, I think that’s neither here nor there.
With regard to 37% of notices not being valid copyright claims, When I first read this PC World article, my inital reaction was: I don’t see how Google evaluate the validity of a copyright based on the information provided in a DMCA notice. For example, neither the presence nor absence of a copyright registration is conclusive as to validity. If Google had conducted a survey of DMCA notices and came to that conclusion, then that is interesting but what was more likely was that the 37% number would simply become a ‘fact.’
Then I came across this article from TechDirt and if you dig through the comments, someone came across what appears to be the original survey that Google cited for the 37% number, and the situation is much more complex. These are findings from the executive summary:

– Thirty percent of notices demanded takedown for claims that presented an
obvious question for a court (a clear fair use argument, complaints about
uncopyrightable material, and the like);
-Notices to traditional ISP’s included a substantial number of demands to remove
files from peer-to-peer networks (which are not actually covered under the
takedown statute, and which an OSP can only honor by terminating the target’s
Internet access entirely); and
-One out of 11 included significant statutory flaws that render the notice unusable
(for example, failing to adequately identify infringing material).
In addition, we found some interesting patterns that do not, by themselves, indicate
concern, but which are of concern when combined with the fact that one third of the
notices depended on questionable claims:
Over half—57%—of notices sent to Google to demand removal of links in the
index were sent by businesses targeting apparent competitors;
Over a third—37%—of the notices sent to Google targeted sites apparently
outside the United States.

So that’s the source of the 37% number. Now, given that the DMCA doesn’t apply to non-US sites, then DMCA notices targeting such sites would be flawed, even if they concerned potentially valid US copyright claims. So an allegation that 37% of the DMCA notices sent to Google are jurisdictionally flawed may be correct, but that they are not valid copyright claims is a mis-characterization.
Also of interest, is the idea that Google receives as many DMCA notices as it does. The survey does raise the issue that on its face, stating that:

These notices are somewhat troubling in and of themselves, as merely providing a link is unlikely to create secondary liability for the search engine, in the first place.)

but see Section 512(d) of the Copyright Act, referring to circumstances where a provider of an ‘information location tool’ might be liable.
See this Chilling Effects discussion of Google’s relationship to the DMCA for more information. There’s an interesting statement in that piece, namely that taking something out of Google’s index is akin to taking it off the Net. Unfortunately, at times, the converse is true as well.
Having said that, there is a problem with DMCA notices based on invalid copyright claims. The idea raised by Google of a neutral evaluating a limited record (analogous to a UDRP type proceeding) is not a hysterically implausible suggestion.
UPDATE: Google’s info page on the DMCA.