I know two examples - one shows no change so far, the other a minor upward change that may be from a different cause. Both these cases were preventative. That is, they were not yet showing signs of a canonical problem in their rankings, but they could not easily fix their server set-up.
I would like to hear from someone who did have a problem with non-canonical urls showing up in the index -- both /directory/index.htm and /directory/ or query strings used only for tracking, for example.
Another success story in this thread [webmasterworld.com], where particleman reports fixing an https/http canonical issue using the new tag.
For my site, WMT was treating www.example.com and www.example.com/?campid=23 as two URL's showing them for duplicate Titles and Descriptions as well as different External links.
After canonical tag was added on the home page, the External links now show only the Homepage (without campid) with no improvement in number of links. However, Content analysis still lists them as duplicate. Guess, will take some more time to update.
implemented this about a month ago.
i had severe home page issues.
ALL had different page rank...
they all now share the same page rank, at PR5, which was my highest rank.
now i just have to learn how to implement ISAPI_REWRITE to eliminate case sensative duplicate content errors.
[edited by: tedster at 8:59 pm (utc) on Mar. 31, 2009]
[edit reason] moved from another location [/edit]
i implemented 2 wks ago - wmt has reduced dup content results in content analysis by half, so far - i think this lags pretty much....
bottom line, no increase in traffic/ratings that i can see.
WMT has again started (rolled back) to show individual external links for the home page as well as homepage with the campid. Guess PR update ripple...
I just saw that IncrediBILL is pushing this tag out to 50k pages, waiting to here the results of that kind of push..hopefully he'll stop by and update us..
we've had over 100k pages up w/ the tag for over 1 month now. going to implement on more sites now, no ill effects...
we already had 301's in place where necessary, but the canonical tag is so much easier for us...
Here's a bad one:
Had a client stuck on a nasty CMS, no access to htaccess, and we're stuck with all sorts of SEO evil (soft 404s, 302s everywhere, dynamic urls, limited header access). So, flip a coin: long, dynamic URLs, or nice, static URLs that 302?
Chose the 302 route, canonized to the shortened URL. Wrong answer, Google freaked out. Had to undo everything, and I'm waiting to see how long it will take before Google responds to the updated tags.
jd_fp - Did your 302 disaster include using the new canonical tag on either the long or the short urls?
Sorry about the late reply.
I targeted the short URLs, all of which 302 towards the long URLs, and google freaked (somewhat predictably, I guess). Re-canonized to the longer, non-redirect URLs, and was restored into good graces.
Of course, now we're back to square one on the SEO front, but at least Google put our ranks back before it played too much havoc on our traffic.