This is what Thomas Hawk said about the Pro accounts on his blog:
"While this might sound really great for today’s free account users, it should be noted that the new free 1 TB account will contain advertising. If you want to opt out of advertising on your free account, you will need to pay $49 per year….
…unless…
you are already an existing Pro account member. While Flickr will no longer offer new Pro accounts, existing Pros will be allowed to keep their Pro account and continue paying $24.95/year for full unlimited high res ad free storage (still the best deal in my opinion)." Thomas Hawk Digital Connection
Sounds like if you have a current Pro account you are better off keeping that.