No, there aren't any known issues with CS5.5.
I would suggest installing the extensions manually rather than letting the Extension manager import them, I dont trust the extensions manager as far as I can throw it....
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.