Search Engine Roundtable noted this one with hints that a new tool may be launched soon to replace this one. I imagine it would be uncharacteristic for Yahoo! to discontinue a service which has been used by millions to check keyword popularity.
Worldwide, there could be a massive switch to other tools. In Hong Kong, this would mean another tool must be used to determine popular Traditional or Simplified Chinese search queries. Other prominent tools such as WordTracker and Keyword Discovery do not provide this kind of feature as far as I know.
But until the new Yahoo! keyword tool is launched, there will be some degree of mourning within the keyword mining community.