ETA: I really should start checking out LJ News. :p Here's the scoop:
We're also excited to announce the Loyalty Userpics program for paid account holders. For every three months that you have a paid account, we will award you one bonus userpic. The bonus userpics will continue to add up for as long as you have paid time, but if your paid account expires, your limit will fall back to the free level. Whenever you renew your paid account, your bonus userpics will be restored.
To reward you for the paid account time you've had in the past, we are going to increase your limits retroactively. If you want to earn your retroactive Loyalty Userpics, make sure you are a current paid account member or that you renew your paid account within the next 30 days (our retroactive offer expires at midnight GMT on April 14, 2006). Permanent account holders will always have the maximum amount of Loyalty Userpics possible, which as of today is 32 (bringing their total to 132), and will accrue Loyalty Userpics at the same rate going forward. Please see the FAQ for additional details.