It looks like the latest version of Chrome is (by default) blocking the installation of extentions that are not downloaded from the Chrome Store.
Chrome Build: 21.0.1180.60 m
Windows 7 64-bit
Help topic Google linked me to when the 1Password.crx was downloaded:
I should add, the steps outlined under "Steps on adding extensions from other websites" on the help page allowed me to install the extension.