An apparently useful application for Android is Instant Heart Rate, which can be installed from the Android Market.
What it does is measure your heart rate using the built-in camera of the phone.
On my Motorola Milestone, there was a serious flaw though. Once you use the Instant Heart Rate app, the camera's brightness will be totally off: all your pictures will be severely overexposed (all white).
A reboot of the phone solves this problem. Inconvenient when you have something running in the background such as a GPS tracking application or instant messenger sessions.
For now, I uninstalled this application.