Thanks to all of you guys for an informative thread.
I have suffered with this problem intermitently with my 02' 3.0d.
As with you guys I noticed better start ups during the cold or after leaving the vehicle for a few hours.

I took mine into the stealer (lol! I like that 1), and they couldn't find a thing just gave me a new 'purse' key (slim black plastic key) and wrote the problem off as my original key having some sort of fault!

Anyway, since reading the ig swicth maybe at fault I am looking into giving this a clean as Supersteve directs failing that maybe I'll change it out.

My X doesn't die as some have described, but it didn't start for nearly 2 days when I first experienced the problem! Since coming out from the stealers (3 months back) I have not had the issue arise until last week. At which point it didn't start on 3 seperate occasions on the same day, very embarassing to say the least! Happy to say that it was limited to the one day, but obviosuly I assume this will get worse and more frequent if left to its one devices...

I will try the contact cleaner route, failing that probably change out the ig switch.

Thanks again for a very informative thread guys! Hope it will help me resolve one of the 3 problems with my X.