When you compare trophies with someone on PSN, a percentage is displayed under both usernames. What do the percentages mean?
(I'm not talking about percentages on each game.)
This is the percentage of you and your friend's current completion for any given level of the PSN's trophy system. It means you are X% through Level Y. You should see a corresponding bar that acts as a visual indicator of this as well.
It's not horribly useful as a direct comparison stat, as your friend could be 25% of the way through Level 12, while you may be 98% of the way through Level 1. You can pretty much consider it negligible because of that.