Another old tutorial I wrote.
This tutorial and sample MP shows you the right and wrong way to go about multi instance monitoring when you are using scripts and property bags. If you are not careful you can end up running way too many scripts without even realizing it. I walk through the good and the bad and also show you how you know you are doing it all wrong!
If you are new to scripting in SCOM then you should read this.
The attached zip has the tutorial doc and MP in it.