I was just working on some performance improvements for parleys while I encountered a big memory leak.
If you run into problems like these (and you will sooner or later :-)) Flex Builder professional saves your day. The profiler alone is worth every extra penny.
Not only should you take care to use weak references with listeners but also watch for your Bindings. If you use the Binding tag their is no way to remove the reference and therefore your objects will never be ready for garbage collection. So i get used to replace my binding tags to ChangeWatchers which gives me the ability to unwatch them. With the profiler it`s really easy to find and fix performance and memory issues like these. I was able to reduce the memory usage by 2/3 in 30 min of work.
These otpimisations are not yet in the current parleys beta version (will be next week) – so watch out for the difference 
So please do yourself a favor and don`t be stingy – get yourself the full monty and buy Flex Builder Pro!
Espacially if you`re a dirty hacker like me Flex BuilderPro will help you improve your skills 😉
I definitely agree about the profiler in Flex Builder 3, don’t code Flex without it!
I use ChangeWatchers quite a bit in my code as well, but I was also under the impression that Binding tags registered with weak listeners so the objects would be eligible for garbage collection? Maybe some quick tests with the profiler can answer that one
I had already bought the standard licence before I realised there we’re two! I was really pleased at how cheap it was until I installed it!
I think Adobe could have advertised the licencing a little better – never mind I can upgrade next pay day