Nice. I think you'll be pleased with it's effectiveness. I haven't had a single spam ever since I implemented CAPTCHA on my blog well over a week ago now. I'm very pleased with the way it's been working, at least so far. There's some that seem to think that it won't work [0][1], and I'm sure that some spammers will figure out ways to get around it, but at least until a better solution is available (I'm hoping to get my site upgraded to Community Server, with built-in comment moderation...the best solution overall I think, soon after v1.0 is finally released) I think CAPTCHA will work great. Blog in peace my friend. :)

[0]: http://haacked.com/archive/2005/01/20/1967.aspx
[1]: http://scottonwriting.com/sowblog/posts/3154.aspx