This more or less reflects what I have been seeing (on a low volume private mail server) but the dropoff for me started around late October with connections staying at relatively normal levels but the amount of spam coming in falling to almost zero.

Curiosity (i.e. tcpdump) turned up the reason - what looked like a spammer 'template typo' that was causing emails to fail relatively silently with a protocol error, so they never got far enough to be counted as anything. It looks like they have fixed it now and are trying to make up for lost time.

I don't know which botnet was responsible so I couldn't say how widespread this was but I don't think it's entirely coincidental.

> Most people in the UK are happy to be profiled in exchange for financial benefits.

I'm not sure this is quite accurate - what proportion of people with those store cards have even the faintest clue what the profiling involves, or even that it is happening?

They will have signed up for the card on the basis of getting vouchers in return for shopping at ther same place. Even if the application form said anything specific about profiling - doubtful, as it would be in terms of 'we may use information' - it would be in the small print, and not many people bother to read that.