I've just added support to my blog for Akismet through the use of this php class. I'm currently waiting on my API key before I enable it.
I got a wordpress.org account before the akismet system was around. So I needed to wait for someone to attach a key to my account.
I've just had akismet block my first spam messages that were getting past my old system. Seems to be working really well. :)
Why do you need to wait for an API key? I just installed it and used one from my WordPress.org account...