Whenever you delete files using the file browsers in Ubuntu, Windows or MacOSX, those files will be moved to the trash folder. So, the first place to look is the trash folder of your current machine.
When one machine receives the message that some files where deleted in another, it will also move the files to its trash. So if you have emptied the trash or for some reason the files are not there, you can look on the trash folder of other synchronized machines.
Finally, if you have looked on the trash of all your devices and didn't find the files, you can contact the Ubuntu One support team telling the path of the folder you need to recover. There is a limited capability of what can be recovered from the server, so there might be cases where some files can't be restored. And only the latest version of the files are stored on the Ubuntu One servers, so it's not possible to restore an old version of a file.
Whenever you delete files using the file browsers in Ubuntu, Windows or MacOSX, those files will be moved to the trash folder. So, the first place to look is the trash folder of your current machine.
When one machine receives the message that some files where deleted in another, it will also move the files to its trash. So if you have emptied the trash or for some reason the files are not there, you can look on the trash folder of other synchronized machines.
Finally, if you have looked on the trash of all your devices and didn't find the files, you can contact the Ubuntu One support team telling the path of the folder you need to recover. There is a limited capability of what can be recovered from the server, so there might be cases where some files can't be restored. And only the latest version of the files are stored on the Ubuntu One servers, so it's not possible to restore an old version of a file.
There is an open wishlist bug to add a trash to the Ubuntu One website: https://bugs.launchpad.net/ubuntuone-servers/+bug/377905