To whom it may concern:
It looks like Seagate Momentus XT is incompatible with some MacBook Pro models (Mid 2009, model identifier MacBookPro5,4, Serial-ATA NVidia MCP79).
The incompatibility manifests itself by the system being hung in I/O - in Activity Monitor both Reads in/sec and Writes in/sec will stay at zero for tens of seconds and eventually the hang will become permanent requiring reboot.
Another possible related symptom is smartctl (part of smartmontools) showing non-zero "UDMA_CRC_ERROR_COUNT", e.g. for a brand new drive:
199 UDMA_CRC_Error_Count 0x003e 200 196 000 Old_age Always - 32529
I've tried shorting two jumper pins as described in the Momentus XT manual to tell the drive to avoid negotiating at 3Gb and force 1.5 Gb instead to no avail - with the jumper in place System Report still showed a "Negotiated Link Speed" of 3Gb.
Most likely related: Ugh, SSDs in the MacBook Pro