"Otherwise they have a very similar method of cloaking detection, a similar policy for punishment, and a similar timeline for reducing the punishment for cloaking… At this point I feel that there are too many coincidences for this to be mere chance."<p>I disagree. The realities of having to work in the real world will tend to push Google and Bing in the same directions, even if their development is fully independent. The possibility of independent implementations of similar policies is <i>not</i> so unlikely that it justifies accusations of copying. I think you need more evidence.<p>Besides, it can't flow along the pathways that were previously established to my satisfaction (YMMV). If I understand it correctly, the Bing toolbar analyzes click patterns to see how pages connect together on the web, Google used the Bing toolbar while making their spiked searches, and found that small amounts of that signal made it into Bing, which was exposed when they created searches by design that had no other signal. I'd lay money the Bing toolbar now has an exclusion for Google (and probably other search sites), if only because Google demonstrated it opens an attack vector from the competition. And I do not think the Bing toolbar could pick up on cloaking like this, because that would rest solely on Google's internal servers. I'm not even sure by what mechanism Bing <i>could</i> be copying this signal from Google.
Redirecting on user agent to a mobile site is kinda annoying, but not against Google TOS. Only if you show Googlebot different content than you would show other user agents (single out Googlebot), is it considered cloaking.<p>You talk of a penalty, where a search engine accessibility issue seems a lot more likely. SE accessibility issues usually translate to all search engines.<p>Besides that there are a few other possibilities that follow Occam's razor and don't promote the Bing-steals idea. The biggest of these would be trends or market changes. If all around the board you get less people searching for your product (for whatever reason), this should reflect in all search engines' stats.<p>It's also perfectly possible that an older niche player cleaned up his/her game, or a new competitor hit the scene. Both could eat up your traffic.<p>Or a webmaster that had many sites linking to you forgot to renew his/her domains.<p>I don't fault the OP for jumping to conclusions (well, maybe a little bit more care would be appreciated); search engines are a black box, and it is all too easy to connect changes you made on the site, to changes in stats. Even when they are not correlated.<p>Next time when you encounter a bump and ask yourself: Did I get a penalty? Really try to pinpoint the problem: Which parts of the site took a drop? Does that site still link to me? Is is a trend, and do last year's stats show the same decline? etc. etc.<p><a href="http://www.seomoz.org/blog/whiteboard-friday-oh-i-got-a-penalty" rel="nofollow">http://www.seomoz.org/blog/whiteboard-friday-oh-i-got-a-pena...</a> can help you with this. Also read up on how to submit a mobile sitemap and have these sites running next to each other without any (perceived) problems: <a href="http://www.google.com/support/webmasters/bin/answer.py?answer=34648&hl=en" rel="nofollow">http://www.google.com/support/webmasters/bin/answer.py?answe...</a>