In my experience, no, not at all rare.Think "plague" and you'd be closer in your assessment of guestbook spam ;-)
In HT you rarely see spam
I was being sarcastic not at you really, more the idea that I don't get spam in HT, which I do constantly.Please don't take offense, I wasn't directing that at you personally.
The constant problem with guestbooks is that one man's spam is another man's treasure, and always causes issues amongst the staff in HT.