I'm using a two-week old HTC Sensation. A number of times now, I've tried to download apps (this is happening on multiple apps, not just one) and although they download, they never install. I can see the download happening and getting to 100% in the status dropdown, but it never continues on to install. I don't get any error messages; it just never goes any further.
This happens regardless of whether I download the app from the Market on the phone, market.android.com on my computer, or the Amazon app market.
Android version 2.3.3.