I’ve been getting a lot of questions about using the tag ‘rel=”nofollow”‘ on both internal and external links.
The best answer I can come up with is to look at the Google explanation here. They say that they don’t follow ‘nofollow’ links and not just not pass on PageRank (there are rumours that this is not strictly true, but I am happy to believe it is true enough).
With this in mind, the new ‘rel=”canonical”‘ header tag can help with allowing Google to spider as much of your site as it can (within reason, they won’t stay for as long as you want them to), but not leave PageRank juice all over the place (messy…).
As mentioned before, even your ‘noindex’ pages still carry PageRank and even though they will be passing a lot of this out they will still retain a bit. So the new tag really helps with large product sites with various results pages and various ways of ordering those results. Basically, you can now get the products pages spidered without dropping page rank on all of the search results pages. You still have to be a tad clever though with your dynamic URL insert into the ‘canonical’ tag.