Been using 1Password across a PC and a couple of Macs myself and I love it.
As per [1] their data format is pretty open and based on the OSX Keychain format. Uses PBKDF2 to generate unique salts/encryption keys per password. Like any password management system, if you lose your master password, you’re still screwed… But (format being open and based on solid standards) it doesn’t appear (to me [2]) to be vulnerable to a similar attack (i.e, an unintentional backdoor password of sorts).
The Windows version must use some implementation of the same backend, since the data file works across platforms (they’re big on the Dropbox sync support).
[2] i.e., with my limited experience with information security, knowledge of some best practices for password storage, and my interpretation of the data format
[1] http://agilewebsolutions.com/onepassword/win