An interesting IS bulletin which was really published by one company. 

Recently, two individuals from USPL were traveling to Belgium on Sabena 
Belgium World Airlines, which is affiliated with Delta Airlines. They were 
seated in row 6 of the plane where seats contain the tray tables in the 
armrest section of the seat. 
They setup their tray tables and proceeded to use their laptop during 
flight, both their PCs began experiencing problems. Apparently the tray 
tables were magnetized, so they will not make noises while stored in the 
armrests. The magnetized trays corrupted the hard drives of both laptops. 
On this particular Belgium flight, the aircraft happen to be a "new" 
Airbus 340, which explains why this has not surfaced until now. The 
problem seems to be with a specific European aircraft seat manufacturer. 
US Airways, NorthWestern and United have no plans to utilize these 
magnetized trays in their new Airbus aircraft. Boeing and McDonald Douglas 
also has no plans to use these magnetized trays in their new aircraft, and 
there have been no reported cases of other types of aircraft experiencing 
this problem. 
The purpose of this notice is to simply make travelers aware of the 
"potential" problem, especially on Airbus aircraft built for European-
based airlines. If the tray table appears to be magnetized (use a 
paperclip to see if it sticks), then I advise people NOT to use their 
laptop computer on these trays.