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How long ago did you make the changes?  You may just need to give the crawlers some time to go through your site again.

Did you double check to make sure that the live pages have the updated meta descriptions?  Check the source code and make sure the new ones are showing, otherwise you probably still have an issue within Wordpress.  Otherwise, just give the crawlers some time.

If this is something you check for often (which it probably should be), you might want to check out a program like Screaming Frog.  That makes it really easy to find 404s and any other response codes.

Amazon can also get away with things that most sites would never get away with.  Google is not about to take Amazon out of the rankings so they get a bit more leeway.

If this is indeed a linkjuice play, I would probably avoid it and just focus on what is going to deliver the best user experience.

I would just make it something that is simple and easy to remember and that people will associate with your business.  I think the branding effect will be much more significant than the seo impact unless you get a great keyword.

I would make sure any links you put in are very relevant and watch out for the anchor text.  My guess is that Google will probably lower the value of those links but not penalize you, but make sure whatever you are doing is worth the risk of getting penalized.

If you just want to see a few users on your site you can try usertesting.com.  I have gotten pretty good feedback from them that I hadn't considered before.  But it is definitely not done on the scale you are talking about for the first part of your question.

http://www.seroundtable.com/google-updowner-ignored-15369.html

Looks like Google is on top of these guys so at least their links won't get you Penguinized.

As long as you think the sitemap is done right it should be fine.

In the short term I would definitely use canonicals to let Google know which are the right pages until you can fix your problem.  Also, have you submitted a sitemap to Webmasters?

I agree that you need to make sure there are other ways to get the ebook (or whatever you are giving away).  It may be hard to believe, but not everyone has a Twitter and/or Facebook, or they may not be willing to use it and you don't want to send a potential customer away frustrated.  But otherwise I think it is a great idea and is at least worth testing.

Amazon can also get away with things that most sites would never get away with.  Google is not about to take Amazon out of the rankings so they get a bit more leeway.

If this is indeed a linkjuice play, I would probably avoid it and just focus on what is going to deliver the best user experience.

The white text on the page is pretty hard to read.  If you definitely want to keep the white on black look, I would try to space out that content a bit more and use a larger font size.

http://www.seroundtable.com/google-updowner-ignored-15369.html

Looks like Google is on top of these guys so at least their links won't get you Penguinized.

I'd be really careful with the directories - make sure you are only submitting to high quality sites.  Being on too many low quality directories is a good way to attract the attention of the Penguin.

I think a press release is a good way to start.  You can have one written about the launch of the site.  Use a high quality service like PRWeb.com.  Expensive, but will only get you quality links.  There is also the chance it gets picked up by some reputable news sites.  That's when you see those beautiful little spikes of traffic in analytics

I haven't actually done this myself but a colleague of mine does it pretty regularly with decent results.  I would only do it for sites that would provide really good links, the ones that give you link juice and also some referral traffic.