The main drawbacks for me is portability and stupidity-proof.
It's extremely annoying, with the current solutions, to carry the db of passwords with you and to have to install the appropriate program to read it.

Just imagine yourself wanting to login to your account on another machine.
> Huh, wait let me plug my USB
> Ah, I need to install the 32 bit version of the program to read the DB
> Oh, I don't remember the password to open the briefcase

In those cases you just don't login at all and wait until you get home.

At the moment I stick with the passwords that are in my head and if I can't remember it there's always the "forgot your password" button.

EDIT: The only good password management tool I use is the one that comes with Firefox sync.