QDesktopServices::storageLocation(QDesktopServices::CacheLocation) + QDir::separator() + "msyncd"; // would be a lot less long-winded than these two

also, you should not be using global statics that are non-POD (and QString is not POD). I'd suggest something like:

static QString syncCacheDir()
{
    return QDesktopServices::storageLocation(QDesktopServices::CacheLocation) + QDir::separator() + "msyncd";
}