A couple of days ago Yahoo! updated their link counts in their very cool Site Explorer tool. A lot of webmasters were reporting HUGE drops in their link numbers, so I ran reports on all of my domains. The results?
An average drop of 18% in the reported number of links. My main site, Web Marketing Now, saw a drop of 4,000 links (from 25,000 to 21,000).
Yahoo! just did an algorithm update, and while this probably has nothing to do with that update, I have looked at what the changes could be and I’m not seeing any consistency in the types of links which were dropped. There is speculation that Yahoo! is no longer counting certain types of links and removed “nofollow” type of links, but that is just pure speculation at this point.
The bottom line is, there was an adjustment, and Yahoo! doesn’t have enough market share organically to really cause too much stress over this.
The main reason I started the SEO Revolution was out of frustration. Frustration at all of the lies and misconceptions that are posted in forums, given as advice in teleconferences, and even taught in live workshops. "So why didn't all of this work?" " Why wasn't my site successful?" " Why am I still stuck in a rut?" 
To this day (April 2011), I routinely use Yahoo Site Explorer to do a quick check on back links. I have yet to find a better way to get a quick survey of what’s been indexed.
For example, one seo guru raved about Majesticseo.com, but I’ve had many challenges with it’s accuracy.