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Although I don't have an explanation as to why your SEOmoz rankings vary greatly every week, I can offer some suggestions/ideas to get over this little issue. Have you tried e-mailing the SEOmoz customer service team (help@seomoz.org)?  They might be able to look into your specific case and diagnose any technical problems. In the mean time, have you tried creating a completely new campaign to see if the same thing happens? What about using the rank tracker that is NOT part of the PRO web app?  It has weekly updates and if the same problem occurs you can try manually refreshing the rank once every day. Lastly, a little more legwork here but you could also try running your rank checker about the same time SEOmoz updates their rankings in the web app/rank checker tool.  Maybe you might see a difference there? Best of luck!

Something that I also look at when checking rankings for different keywords(the very competitive ones esp) is to look at when google last cached each of the top results - I've found that this can sometimes lead to changes in rankings since our page has not been crawled in a few days and the few above ours just got crawled. Just a thought

Definitely explains it! Thanks

Fantastic. Thank you so much.

if we just duplicated our homepage, would we not get penalized? You would not receive a penalty as long as the SEO was handled properly. If you have a page mysite.com design for the US and another page mysite.com/uk designed for England then search engines should understand clearly that each site is designed for a particular country, even though they are all in English. A few added points: a ".com" site is not thought of as a US site automatically. Google makes that determination based largely in part of where your site is hosted. You can also set your site's target country in Google WMT to avoid any confusion. there is a langauge meta tag which is something like "EN-US" for the United States and "EN-GB" for England. By setting that tag you will help search engines understand your target audience. be certain to localize your page. For example the US says "center" while English people say "centre". There are different monetary units, systems of measurements and phrases associated with each culture as well. if our host was able to simply put the pages on different servers, would that be sufficient? No. A different server with the same host would not be sufficient. You need to change your C-block and usually a host will retain the same C-block for all of their servers. having a page targeted at say, Mexico, loading from a UK server may not be great for page load times. True, which is where cloud hosting is very helpful. The prices are fairly reasonable and it is an option you may want to explore.