It doesn't sound like it should be a positive announcement but the volumen of emails that are spam has droppped significantly. While a part of this may be due to better informed users and improving spam filters, mosto of drop is attributed to cyber-criminals moving onto other methods.
This is the first time in 12 years that less than 50% of emails are spam. Spam now only accounts for 49.7% of emails, still a massive amount.
The report from symantec only covers their anti-virus clients but is one of many strong indicators that the absolute amount of spam is dropping. But other forms of malware in Symantec intelligence report have increased indicating that the decline in spam might be more directly linked to scammers moving to other methods rathering the increasing effectivness of anti-spam activities.