While Akismet does work already pretty good as a blog spam comment filter, it is sometimes necessary to drop some spam comments manually into the wordpress spam folder, so that Akismet can learn about new spam to filter out spam comment even better in the future.
I´d say that Akismet can already filter out 95% of the junk comments but there are always some comments coming through, which I would call the 5% of the new blog spammers who are not in the list of Akismet´s database yet. It is not much work to teach Akismet that it is a junk comment. Just mark it as spam and the junk comment will go into the spam filter. I suggest you never to delete the spam section in the comment section of the WordPress dashboard, as it seems to be the brain for Akismet!
I also suggest that you do not let all comment go through on your blog. Moderate every comment. It is easy to set it up to moderation. Just click on “Settings” in your dashboard and then on “Discussion” and look for the “Before a comment appears” section where I strongly suggest to use both “Comment must be manually approved” and the “Comment author must have a previously approved comment” options. That´s the way to be on the safe site that no spam can come through!
Even if you did not have many commenters on your blog, never do let a spam comment go through nevermind how nice the comment is written. But in most cases they are anyway not pretty good. They are often very strange written and most of the time not even related to the content of your article. But the biggest problem with them is that they could place a link on your site that will hurt your project! There are several reasons why you do not want gambling, insurance, porn, weight loss, Viagra or any other spam links on your blog. Google does hate them! And Google could even punish your blog if you have them places on your blog, even if it is just a comment. Point. You do not want them as they give you no benefits.
Experienced bloggers can spot spam comments in a millisecond. But everyone has to start and if you are new to blogging, it might be that you won´t spot them so fast. This is one of the reasons why I will create a series of articles about spam comment examples. But another reason why I do so is, that they are often so obvious to spot and funny that I really could create a comedy section with it. This is why I will publish some screenshots of them in the future (for sure censored). I think I will call the series “Hilarious Spam Comment Examples” and you might want to check it out. :)