Interesting thread. I also think it's Pakistan and India and they don't only do it on forums but also on online job sites like oDesk.
Indians are the biggest spammers anywhere they live on the planet. But, at the same time, not many forums online would get the kind of traffic and loyalty they get if it wasn't for Indian visitors. Whether it is Soccer or Programming, and forums like this one or any other one Indians have a way of making that online space their home.
Definitely India. They are very shifty, not only at the forum but also at the daily life (office, etc)
Probably because forums don't get a lot of spamming from the UK. According to statistics I've seen, it would be China.
From experiences here, the number 1 is from India, not trying to stereotype any country but just stating the facts. Hopefully, those from India can persuade their countrymen not to spam and maybe report the spammers to us so that we can delete the trash. We respect all countries, fact of India being number 1 can be because they do have a large population that speaks English. But lets cooperate and ensure that our forums are spam free and spammers from all countries are kept at bay.
Check out this one guys. A list of top 10 spammer countries http://www.spamhaus.org/statistics/countries/
Spamhaus mostly tracks email spam (not forum spam). For email spam, yeah... I would suspect the United States is the worst.