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Hi Caroline, links that are no followed don't directly pass any value in the form of link juice which has a direct impact on SEO and search rankings. However they are still very valuable as they can be linked to by countless people (on their own websites and guest posts meaning potentially followed links) that become aware of your links through social exposure on twitter and similar. I did a bit of digging as I knew there was a decent Q and A on this here you go - http://www.seomoz.org/q/value-of-twitter-links

We did not have an update between February 27th and yesterday. If you run reports now, you should see an update for most metrics (besides anchor text). We have a blog post about the latest update at http://www.seomoz.org/blog/mozscape-update-our-largest-index-yet-159-billion-urls

Definitely eliminate personalization, as alsvik said. Beyond that, though, there are still other factors (Location, I.P address etc.) that you need to account for. The best way I've found to handle it is to forget the idea of a "true reading". There are too many variables to eliminate in the real world. Instead, keep your measuring consistent and prove value that way. If you measure in the same way each time you can demonstrate an increase or decline in rankings, because the variables will always be the same The various tracking tools, while not perfect, will eliminate some of the variables, and will certainly give you a consistent read each time. From a client management perspective, it's more about setting client expectations than anything else. You need to discuss the fact that results may be slightly different when they check. You also need to explain why. Once you've done that, you need to get your client to agree to the process you'll be using to track rank. If you use SEOmoz rank tracker, or Raventools, or whatever else, then get their buy-in that that platform is the one you'll be using to measure the effectiveness of your work . If you don't, you're likely to end up playing the "I'm not ranking where you say I am" game. Edit: If you're tracking rank manually, then consider looking for something like the Bruce Clay toolbar, which will let you run searches via proxy.