The loss of an aircraft and crew from any fleet is sad. As for worrying, of all the hundreds of thousands of sorties flown by the Nimrod fleet this is the only one lost due to a fuel fire. Previous losses are attributable to other factors discovered during the Boards of Inquiry, some of which have led to mods to the airframe or systems.
There will probably be a programme of inspections [I would guess tied in with one of the deeper servicing schedules], just to check out the likely areas that led to this tragedy.
I doubt whether crews will be worrying or sweating over flying the Mighty Hunter for fear of a repetition. My guess is that this is a tragic one-off failure.