At least for now, the Overture Keyword Selection Tool is now back online, I think as of yesterday some time.
Monday we reported some sporadic reports of the tool going offline for a bit. Then on Wednesday we reported Yahoo!'s statement saying that the tool is basically dying and that Yahoo! is building a new one.
I suspect they fixed some of the issues now.
Forum discussion at DigitalPoint Forums.

Comments:
Jon West
02/03/2007 02:55 am
Thanks for referencing my thread. Wish you had linked to my blog post instead. ;)
Barry Schwartz
02/03/2007 11:20 pm
I am sorry, you have to read the submission requirements... http://www.seroundtable.com/thread-submit.php And FYI - there are tons of threads about this. I am sorry.
No Name
09/12/2008 04:36 pm
I know exactly what you mean...it's been a nightmare!! But i've been fortunate as my site still gets alot of traffic because my products are so good :-) http://maybewhatever.com/
No Name
09/12/2008 04:48 pm
eBay...Who needs them??I mean we can practicily sell anything we want online for example i've got an ebook for $2.99 called Affiliate Marketer’s Handbook and it can teach anyone how to make extra cash online!
Stephen
10/17/2008 03:48 pm
It's funny the way it keeps changing...seems like it's a daily occurance!!