There have been a number of threads regarding the need to provide password/pin security for particular apps on the Android platform. The need for such protection ranges from corporate concerns about email confidentiality to privacy issues that individual users may have with regard to messages, emails, photos, etc.
There now appears to be a set of applications from either one or two developers (The apps appear to be so similar that I suspect they're from the same source.) that provides that security.
The apps are:
() Gmail Protector
() App Protector and App Protector Pro
I can't comment on the difference between the free and paid (Pro) version at this point but App Protector appears to do what is intended. And as far as I can tell it remedies a limitation with the original "Protector" app that turned off the lock on an application once opened until the phone was rebooted.
By default, the app protects any applications the user designates by imposing a numeric "pin" before the application can be opened. It also adds such protection to "Settings" and any application task killer to prevent the Protector from being disabled.
So for those who send/receive confidential emails or have other applications for which they wish to maintain private access for any reason, these apps appear to resolve a major security hole for the Droid.
Only one slight concern that deserves mention here. The same developer (Carrot App) markets an app (disguised as a tip calculator) that allows spying on SMS messages sent by a phone by forwarding all SMS messages via email to someone else. Although such an application might be argued to have a legitimate purpose in terms of parental monitoring, it frankly bothers me that the same developer is marketing an application to protect confidential information on a phone. YMMV and as far as I can see, there is no reason to believe that the password protection program has similar functionality.