I like the Windows Live Toolbar, but one thing I miss from its predecessor, the Desktop Search Toolbar is auto form fill. This allows you to capture stuff like your email address, mailing address, etc. in a password-protected file on your local machine and when the toolbar detects a web form, you can with a single button fill in those forms.
I found that with Windows Live Toolbar, you have to install the Form Fill button separately. But trying to do that from the options dialog consistently failed with an obscure Windows Installer error.
I used to work closely with the Windows Installer team when I was the development manager for Office setup, so I know a bit about debugging failed Windows Installer installs. The trick is to get a verbose log of the install.
I did this and found this error message in the log:
DEBUG: Error 2738: Could not access VBScript runtime for custom action
The installer has encountered an unexpected error installing this package. This may indicate a problem with this package. The error code is 2738. The arguments are: , ,
MSI (s) (6C:CC) [12:06:01:411]: Product: Form Fill (Windows Live Toolbar) -- The installer has encountered an unexpected error installing this package. This may indicate a problem with this package. The error code is 2738. The arguments are: , ,
Next step: Search the web for the text "Could not access VBScript runtime for custom action". I found this post which points out that for some reason the VBScript runtime is not registered on Vista (I'm assuming this is probably a security thing to prevent scripts from being easily run).
Sure enough, registering the VBScript.DLL did the trick and I now have Form Fill!