Some “Flash haters” claims that deeplinking in Flash & Flex is one of the reasons that these techniques is not suitable for large scale projects for the web. Yes, this is true, if this wouldn´t be possible it would be a problem for dynamic and highly interactive sites that most Flash/Flex sites are. But, this is possible and very simple! Hurray!
I recently did this on a Flex project and it was a lot easier than I imagined. There are a couple of alternatives for doing this in Flash/Flex 2 (Flex 3 is already equipped with it). I choosed between UrlKit and SWFAddress and ended up using SWFaddress since the implementation seemed a lot easier and there are some major sites out there using it. Both these libraries are free but if you end up using them in a commercial project I think the authors would be greatful for a donation.