cwatters raises a very good question - signal strength from wireless LAN equipment (which can include PDAs as well as laptops) is several times that from a mobile phone (but on a higher frequency, 2.5GHz). Bluetooth is a much weaker signal, designed to operate over distances of a few feet/metres. Wireless LAN capability is now being built in to laptops - it can be software disabled, but how many users will know/think to do that?
Do galleys make use of microwave ovens (which also operate at 2.5GHz)?
As I've observed before - while I make every effort to switch my mobile off, very occasionally I forget. If I remember during the flight, I'll get up and switch it off, but what if it's in my checked baggage? With dozens or even hundreds of mobiles on every flight, it's a virtual certainty that one or more will be on (that doesn't excuse us from making every effort to switch as many off as possible).
If this is a real problem then we either need:
(a) a foolproof detection system (difficult with devices that by design are radio-silent for minutes at a time); or
(b) hardened aircraft avionics that aren't affected (unlikely to be retrofitted).