Here is a cool tip from Programming Flex 2. This code is from a Flex 3 project. I believe the syntax is the same for both versions of Flex. Notice that the repeatCount attribute in the Sequence component definition is set to 0. This will repeat the Effect until you call the end() method on the Effect. In addition the repeatDelay attribute can also be used to specify a pause between the cycles of the loop. This is a pretty simple example but illustrates the concept.

View example:
http://seantheflashguy.com/flex/Flex3EffectsExample/Flex3EffectsExample.html

Here is the code:
http://seantheflashguy.com/flex/Flex3EffectsExample/srcview/index.html