The thing most people have been worried about following the PSN attacks, and rightly so, are things like email addresses and credit card details. On a more trivial note, though, people have also been worried about their trophy data and friends lists. Well, don't!
Sony has come out today and said that both your trophy data and friends lists are safe and sound, and once the PlayStation Network is back up, they will be too. What's more, any singleplayer trophies you've unlocked over the past week will re-synch once everything's up and running as well.
As for friends lists, they're in no way affected. Nor will PlayStation Plus cloud saves, if you've got any.
Q&A #2 for PlayStation Network and Qriocity Services [PlayStation]