Ramesh,

It's not a problem that you site opens when you type in the IP address--that's normal.

So it seems the link network became a weight around your neck, so to speak.  If you didn't receive an unnatural links warning in GWT then it was an algorithmic smack and if those links were, in fact, the issue, then you may just draw a new baseline at you current levels and start working your way up again from there.

Well, if they were all nofollowed, it would be hard to suspect that they were the problem.  Still, thatsalotta back links! I think it's interesting that the other US sites didn't take that  same hit and that some of their traffic increased--almost as though the links to the main site disappeared and the link juice consolidated on the remaining links to the other US sites.

I've made a couple of mental guesses but there's just too much going on there without enough detail to put an educated guess down in writing.  I'd like to know if the links between the sister sites were spread evenly among all the sites, if the sites are all in the same market, and the outcome of the hunt to discover whether all the links were all nofollowed or not before taking a stab at it.

To start out with, I'd think more along the lines of unique content for each product vs. for each keyword, but yes  you want unique content for each of those pages and each page should be focused on one keyword.

Gregory,

Matt Cutts has said that it doesn't matter algorithmically--essentially, Google deals with both as though they are one. I'd go with whatever your web server defaults to serving.  If visitors normally get a trailing slash, canonicalize that, if they don't canonicalize on the URL without the slash.

http://www.mattcutts.com/blog/seo-advice-url-canonicalization/

Eric, give this a try:

Take one of your long tail keywords, plug it into google search and review each web page that shows up in the first page of results. Note how focused is each one is on that keyword--at the exclusion of any other keywords.  Do other searches on similar long tail keywords on your list and see if the same pages show up in the results or if a different set of pages show up in the results.

If you compare all of your keywords to what shows up in the search results, you're likely going to find a couple of things.  1) You're going to get a tiny taste for how much time and effort it's going to take you to create content for each of those keywords; 2) You're probably going to find that for a majority of your search terms, different sites show up for each search; 3) You're a bit overwhelmed at the realization of how much content you're going to have to create.

If that's the case, do yourself a favor and pare down your list of keywords to a small fraction of the total and work with those as a starting point.  Create your content for what will be your most profitable terms, keeping in mind that the whole purpose of its creation is to get your target audience members to engage with it in some fashion.  Work in your content for your longer-tail keywords to help bring in traffic for those terms as well as to provide ranking strength for your money terms.  When you've got a good grip on that, start branching out into you next tier of keywords.