Spam is a huge problem, I can't believe how many spam messages I get. I know that when I was a JDP lead (which stands for Joint Development Parnter), I essentially did the VAR work for a company running beta SBS 2003 software in order to put the product into product before we shipped it. Their biggest complaint prior, and biggest win with SBS, was the amount of spam they reduced.
I found it cool today that Microsoft Outlook 2003 is the Best Spam filtering program available... at least according to this study.
Knowning that Outlook uses the same filtering as Exchange, you can totally use this to sell more copies of SBS! (is my agenda that obvious?)