With the PlayStation 4 launch Sony promised to increase the friend limit on the PSN from the present 100. A week ahead of time they did just that, up to. Up to 2,000 people can now be on your PSN friend’s list.
Now the network can handle up to 2,000 friends as will the PlayStation 4 when it launches. But the PlayStation 3 will continue only to support a list of 100 names. It will automatically filter the friends list when you play on a PS3. In other words it’s more about displaying the names than anything else. You can also set and lock a pre-determined friends list to be used when on a PS3.
(via EU PlayStation Forums)