When Does Lead-Free Matter?
Aside from the RoHS stuff mentioned, in our lab we use lead free solder for high temperature circuit work, we tend to operate diodes and JFETs up to around 450degC and we've found leaded solder can't take the heat. Of course without the lead the solder is harder to work with but the result is that we can test circuits at high temperature without having to make mechanical joins between components, which is the alternative.

Oh, and although you can't use leaded solder in Europe for commercial products you can in military stuff - I think the theory is that military people don't tend to lick circuit boards but there is always the risk that a toddler will in consumer stuff :-)