I got this anonymous comment yesterday, on a really old post, below:
"Tabor, thank you for correcting me. I should not be commenting at 5:30 in the morning. My daughter is always telling me to PROOF READ." This was followed by a link to some furnace ad! (Furnace Calgary Prices Calgary)
This was an older post written after my first trip to Calgary Canada and I guess the business model is to search blogs for city names?
I do allow unmonitored comments for the first week only after a new post. This usually means only one deletion. After that comments are held for moderation by me. That seems to allow me to screen most of the "scrap" from the real thing.