In the newest PSN FAQ blog, Sony have revealed that they have talked to Treyarch about the double XP weekend which PSN users were unable to take advantage of. Treyarch has ensured that PSN will get another double XP weekend as soon as possible.
Here is the relevant part of the PSN blog:
Q: What about the Call of Duty: Black Ops Double XP weekend that was missed while PSN was down?
A: We have been in discussions with our friends at Treyarch, and they have ensured that all Call of Duty: Black Ops fans will get an extra Double XP event as soon as PSN comes back online. We don’t have details on timing just yet, but look forward to an announcement as soon as we have news.