I don't like any application that doesn't use the system chrome. This includes e.g. WLM and older versions of WMP (where I always turn the chrome on first thing). I also greatly dislike that all of the Silverlight 4 OOB apps I've seen so far use
a custom chrome (I'm not sure if they can have the default chrome or not).
If I used Twitter (which I don't), I would likely not use this app because of its use of a custom window chrome.
I don't mind a custom window chrome, as long as everything is consistent, and custom