As I also saw a significant increase in the amount of Spam being seen, I investigated a bit and found that the majority of the new spam was coming from 10 or so server farms. Each of the server farms were easily identified as using the same first 3 octets of the IP address. I created an account level filter to discard all traffic from these 10 server farms and the spam storms were pretty much eliminated.
It is also interesting to note two other behaviors of the "NEW SPAM". The domain names were all of the newly released variety such as .racing, .win, .date, & .review which also offers a great way of filtering out the spam using Spam Assassin or account level filtering.
The other behavior was that the SPAM Storms were coming in groups from specific server farms. I would see a group of 50 to 60 spam mails from a similar IP range, then a lull for some time, and then another spam storm from a completely different IP range. Again, after watching the IP addresses for a while, it became evident that the same limited number of server farms were involved in the spam attacks.