Large numbers of users are reporting two major problems with the Android Market.
Firstly the complete disappearance of apps from the market (including wildly popular application such as the free FBook Facebook application and the paid MyBackup Pro backup application). Upon a search in the market, these apps simply don't appear, and nobody seems to know why. Over on the official Android developer support forum, developers are reporting that their apps have indeed gone AWOL (and therefore stopped receiving downloads), and the big G seem to be doing little at this time to reassure developers.
Second comes a problem (as pictured here) which seems to be affecting only some users on some devices / versions but is no less serious. In a rather bizarre kind of way, some Market servers almost seem to have got out of sync. Users are unable to download some free or purchased applications because the Market front end version information mismatches what is actually on the server - therefore when the client tries to download the application, it gets a 404 and the feared ' Download Unsuccessful' message appears. I personally am experiencing this right now on my stock Vodafone HTC Magic, trying to download the Record It application I purchased! The thread about this problem on the official Android developer support forum has 101 replies at the time of writing but again, no resolution. Note the version numbers mismatch in the image below!
Are you experiencing either of these issues? Reply here!
D/DownloadManager( 3626): http error 404 for download 21
I/vending ( 3253): com.android.vending.AssetDownloader$DownloadManagerBroadcastReceiver.getDownloadStatus(): Unexpected status from download - 404