Personally, I get uncomfortable if the temp is >=50.
I had a temp sensor read 61 this morning but when I felt the drive it was no where near that hot, so I suspect it is a faulty sensor. At those temps the drive will be hot to touch, if it is not then your sensor might be faulty and I wouldn't worry about it.
If it really is that hot you should look at mounting a fan pointed at the disk. Most cases have a mounting point near the hard drives.