The official Pokémon GTS website has posted a notice that it will close at 11:00 a.m. PST on September 14th, 2010. With Pokémon Black and White being released a few days later in Japan and the coinciding launch of the new Pokémon Global Link website, the closure of the Pokémon GTS website seemed eminent. Below is the post from the official site.

Thank you for your interest in Pokémon and the Pokémon GTS website.

The Pokémon GTS website will close at 11:00 a.m. PST on 9/14/10. Although the website is closing, you can continue to use the Pokémon GTS service to trade Pokémon in your video games.

The Pokémon GTS website is closing, but there is a lot of Pokémon fun and excitement on the way. Stay tuned to Pokemon.com for the latest news!

Source: http://www.pokemon-gts.net/info_close/en-US.html

Aw, I was enjoying seeing the stats. Especially how HG/SS increased the demand for it's Pokemon.
I wonder if they can compile data for all time.
That'd be neat.