Hi there,
I heard about yahoo close site explorer, Google also close Google buzz, and also Google make Google analytics premium version. SEO people work hard for understanding Search engine's Algorithms. And they will understand the algorithm then search engines are update their criteria or shut down the most useful services for SEO.
What you want to say about it?

Larry Page has taken this decision, services which are incomplete are being shutdown.

Because Google always gives the best results and every site targets that.

I think we doesn't need to worry about it, we just need to concentrate about what we are doing. Just do your good work, leave the rest of the part for your destiny.

Ya, its true that yahoo close site explorer, but same time it improve itself. So, if search engine make any changes in its algorithm then also first we need to understand it and treat the site like that.
I have not seen any major changes in search engine algorithm.

HI
this is why SEO is challenging , one need to keep changing all the time, because search engines are getting smarter day by day.