It's stored in ~/.trophease_account (this is a text file, with the email address and password on one line each. There should be an 'e' before the email address and a 'p' before the password, but you can check that they're right with cat ~/.trophease_account, or just rm ~/.trophease_account and let it prompt you again.)

I'll add the option for other accounts etc later.

Incidentally, are you in the EU PSN zone? Are you able to login to https://secure.eu.playstation.com/psn/mypsn/ successfully in a browser?

Ohhh... PSN maintenance today. I can't log in at the moment either. Doh!