Well respected SEO Jill Whalen who runs the High Rankings Forum recently upgraded the forums to the latest version of Invision Powered board software and see said soon afterwards traffic increased 50%.
Just compared the organic Google traffic which came directly to forum pages for the past 2 weeks since the new forum with the new "SEO friendly" URLs in place, and was surprised to see that the visits are up 50%.
Interesting. Will see if that's just somehow because it's all new, or if it will remain that way.
I don't think anyone should be telling people that changing URLs will lead to even a temporary loss of traffic. If 301's are done correctly and the overall information architecture of a site isn't changing, no organic Google traffic should be lost. Most likely it will be gained.
Now, who knows if it is the "SEO Friendly" URLs, although keywords in URLs do help, were the main impact here if any. 50% increase is a huge increase. I wouldn't be surprised to see traffic patterns level back to where they were or dip slightly for a bit and then go back to where they were over the next couple weeks.
The cool part of this software was that it was intelligent enough to create the 301 redirects. Jill said, "this software seamlessly created all the 301's," and she said they worked.
Congrats Jill, I hope the traffic continues to climb!
Forum discussion at High Rankings Forum.