Possible Problem in Future
This isn't a bug report but more a future warning.
The 1Password Windows Installer checks if chrome.exe is running and asks you to quit if it is, that works fine.
The current Dev version of Chrome (12.0.712.0) contains the following about:flags entry:
Check for known conflicts with 3rd-party modules.
Enables a background check that warns you when a software incompatibility is detected (i.e. 3rd-party modules that crash the browser).
Which means even when the browser is closed, chrome.exe is still running and I had to disable that setting before 1Password would run the installer.
I know Chrome Dev version isn't supported, but as I say this is more a warning of a possible future problem as Dev will eventually become Stable and the about:flags option may become a default.
Possibly a similar issue is that I believe the Google Cloud Print feature also keeps the chrome.exe process running in the background and I believe that feature has already hit the Beta channel and maybe even stable.