AJ – the libwww scripts I see hitting my site hit all sorts of urls, not just comment and trackback urls. Even non-existant urls, looking for an exploit.

I think a huge majority of them are not trying to spam, they’re trying to break into my site. I’m not worried that they’ll succeed because I try to keep up to date but it’s a useful way of stopping them before they hit any php code.

Dan – exploits, almost all exploits as I said above.
I actually added a check for Opera 9 to my comment form but I dump all the comments stopped in a file. Check it out here: http://ocaoimh.ie/spam.txt (for the time being, will be removed!)