I've complained about this before. I keep reading that spam is automatically deleted after 15 days. Sometimes I don't even get 15 minutes. I check Akismet two or three times per day at the most, but it's usually already empty...and the Akismet count has jumped up. I am finding my own comments and comments of regular commenters in there...and sometimes I am missing my own comments and Akismet is empty. Friends email me to tell me that their comments are never posted...and, again, Akismet is empty. I would certainly like the opportunity to decide if I would like to scroll through the garbage once in a while to see if there's anything legit in there.
I don't get 15 days before spam is deleted and I don't believe Akismet is "trainable" to recognize regular commenters. Grrrrr.