Logging the time that a document is open

I would like to log the amount of time that a form is open and was wondering if there was a simple way to do this. Any help would be greatly appreciated!

Subject: Logging the time that a document is open

The only approaches that I have heard for this are fairly processor intensive. You can create and document on PostOpen and QueryClose (or maybe just on QC) noting the time, unid, username, etc. If so, you might want to store these into a database all by themselves. We implemented a tracking solution kind of like this, but it only did the logging IF a flag was set in the document.