When you setup your phone your created or logged into a HTCSense.com account. HTCSense.com provides cloud based exclusive content such as additional skins, ring tones, and notification sounds just to name a few things. On your phone you also have an app called HTC Hub that provides you the ability to download that exclusive content directly from your phone.
That explains the basics of what HTCSense.com and HTC Hub provides you.
Since this last system software update 2.3.3. yesterday the skin I was using which I downloaded from hub has vanished from my phone and the hub site...there were 4 to choose from and now only 3...its was the purple one. Any body else notice this?