I'm Under OS X 10.8.2
Today I received an update about skitch. them I clicked the update button. the update process started.
until the progress bar reached 70% it give me an error "Skitch failed to download, Use the Purchases page to try again." them I went to the Purchases page, it give me a red text waring. "an error has occurred" I clicked the INSTALL Button again. it give me the progress bar again but for about 1-2 seconds.
the progress bar is about 80% full but reported "12.88 MB of 12.88 MB less than a minute" them the same error again "Skitch failed to download, Use the Purchases page to try again."
Now I wonder that can I do?
Clear the downloaded cache them try again?
but where is the cache?
I googled there is no Appstore folder at ~/Library/Application Support
Actually I've tried delete all the content in ~/Library/Caches/com.apple.appstore before you told me.
but it's not solve my problem the Skitch progress still at 80%. and could not be downloaded again or be canceled.
I googled for another hour... the solution is to use the activity monitor to monitor the app store's procress. download a new app to see files opend by the app store. Finially I found the location of the real caches!!!
for me it's
I did rm -rf * under the folder them download again. Problem got solved!