Products/storage limits doubled as a result of our Facebook giveaway promotion would remain at that level indefinitely. :^)
Bear in mind this is a one-time doubling that only applies to your the limits on your current plan. If you switch to another plan level later, the limits for that plan would not be doubled. E.g., if you're on a $5/mo plan with limits doubled to 20 products and 100MB due to your participation in the promotion, then in order to get higher limits than that, you'd need to upgrade your subscription to at least the $15/mo level (40 products+250MB) or higher.