They replied to my ticket after five days, which I suspect only happened because I DM'd them on Twitter. It took them four more days to actually resolve the relatively straightforward problem (returning the XRP I had accidentally sent to the BTC/USD deposit address).

When I last needed to contact them last August, someone replied to the mail I sent to their support address within three minutes. To say the service has deteriorated since then would be something of an understatement. I won't be using Bitstamp again unless I hear that their support has improved significantly.