Tin whiskering isn't the only problem with the new solder formulations. The lead-free alloys tend to be much more brittle than the standard Sn/Pb solder, and the joints tend to crack with repeated heat/cool cycles. The problem is exacerbated by the use of surface mount components, which have no wire leads to absorb the stress.
Microsoft is learning about this the hard way with massive field failures on their "X-box 360" videogame systems. The lead free solder joints are failing, prompting LOTS of warranty repairs.
