It is always a pleasure to come back from holidays and read comments on your blog. However, not all comments are worth spending time. An example of undesirable comment can be found here. After a first read, it already sounds like a strange comment. Expression such as Hey buddy! make it feel that it is spam. If you go deeper in the text, you can see that there is no personal information about my blog or the topics I cover. This is typical of spam comments.
However, deleting a normal comment may be annoying, especially for the guy who posted it. If you want to avoid the extremity of word verification process or comment moderation, a simple solution is to use Google. Just copy/paste the first line of text and Google will mine the web for other similar comments.
In the case described above, simply put the first sentence (using quotes to get the exact match) and Google will link you to this site. You can easily see that the first comment is exactly the same and can therefore be safely considered as spam.