Probe & Drogue vs. Boom
Having done them both from the receiving end, p&d in Lightning, Tornado and Typhoon and boom in Eagle I thought I would throw in the following observations about the pros and cons of each.
Probe & Drogue
Pros: Once contact established you have a much greater (relative) freedom of movement i.e. you can drag the hose around a fair bit before the tanker crew start bleating or the probe starts complaining. You can get 2 fighters plugged at the same time. You have a redundancy should one hose fail or have a probe tip left behind in it.
Cons: Slightly more tricky to make contact particularly for the inexpeienced and particularly in turbulence. Lower flow rates than possible with the boom, therefore longer in contact.
Boom
Pros: Higher transfer pressures/rates (providing the receiver can take it - not all can). Nice traffic light system that the "boomer" can use to guide you into the correct position. Secure intercom with the boomer once connected to allow you to have a nice chat..
Cons: Very little freedom of movement when in contact, quite demanding. Two people are involved, the boomer "flies" the boom and extends it into the recepticle and the pilot puts the jet in the right place. No redundancy.
Flying Lawyer is absolutely correct in saying you use reference marks on the tanker to position correctly for the contact. You can always tell when someone "sneaks a peak" at the basket and probe tip at the vinegar strokes - it all starts to get a bit wobbly.
Cheers
tarnished