50˚C isn't that bad, especially if it's in active use. The Western Digital 320GB in my former mid-2007 24" iMac ran in the high 50s depending on the season and the ambient temp, level of activity, etc. The 1TB Seagate in my i7 runs far cooler. It is currently at 23˚C but I am just starting to heat the room in the morning.
You're certainly not in danger of heat-related failure on a HD at 50˚ nor is it any cause for concern.