The official Dropbox 23GB HTC promotion will not start until sometime early this month, when the devices are released. To earn the extra 23GB of extra Dropbox space you will need to link your HTC Sense 4.0 device to your Dropbox account and complete “Get Started.”
The method to earn 23GB that is being circulated on the XDA Developers forum and on other blogs and forums is illegitimate. We plan to remove any space received using this method.
Downloading apps from unknown sources is not a good idea, as they might have been modified to include malicious code. We strongly recommend that you only install the Android Dropbox app via Google Play (formerly known as the the Android Market) or from official download links on Dropbox.com.
I hope this helps.
best,
Sean