I refer you to the techdirt article linked above. If you upload a KeePass file to dropbox now, you may be vulnerable to a way of cracking keepass files available at some future date.
Yup; but I'd say you're letting the perfect be the enemy of the pretty damned good.
KeePass' encryption is quite solid -- if it starts to show some cracks in the face of quantum computers or whatnot somewhere in the future, I can always upgrade and change my passwords so the old database isn't valuable any more.
That'd be a PITA, but I don't expect this to happen -- nor for the govt to come up with a huge vulnerability that no one else sees -- so that's the kind of bet I'm comfortable taking.
